We know from [Magic Arcana of 25th October] that the Rakdos are in Dissension. That's one Black-aligned guild, and there are only 2 left after Ravnica. Therefore, the Orzhov Syndicate (BW) must be in Guildpact. By the same reasoning applied to White, we then know that the Azorius (WU) are in Dissension. The only colour not so far represented in Dissension is Green, and we have two allied guilds already; so it's reasonable to assume that the third is the Simic (GU). That gives:
Rakdos (RB) Azorius (WU) Simic (GU)
The logos on that page appear to be a wave with things growing on it, a circle on top of a large triangle, and a flaming anvil or skull. These are almost certainly Simic, Azorius and Rakdos, in that order.
Discussion further down the page, if any is forthcoming. --CH
I also reckon there'll be ten. This ties in with there being 15 extra cards in Dissension. But I don't think it's been confirmed what rarities those extra 15 cards are - I'd think 15 rares would be unlikely, though, as that'd make the #commons/#uncommons/#rares be 55/55/70. I'd think 60/60/60 or 55/60/65 would be more likely. Note that Guildpact only had six non-monocolour, non-guild-aligned rares: the five Nephilim and the Sword of the Paruns. [We've been told] that there'll be one more gold rare for each Dissension guild than there were for Guildpact's guilds; that eats up three of the six "special" rare spots, leaving (two plus however many of the 15 extras are rare) for split cards. So there's not even room for ten split cards at rare unless there are at least 68 rares or they remove some monocolour rares, which Aaron sounded unwilling to do. Or unless he was being exceptionally sneaky with his phrasing and including the rare gold split card that features the Simic (probably GU/RU) as one of the Simic's gold rares.
If we're right about the 10 splits, then there are two Simic splits - Simic/Izzet? and Simic/Golgari?. Which means that "one more gold card" isn't enough. --CH
This all seems to imply to me that, although some of the split cards are rare (at least five), some of them may be uncommon or even common. Which would be very cool. --AlexChurchill
We've got an Orb of Insight for Dissension. Interesting results:
comes - 64. I can't think of many uses other than "comes into play", and that's a lot of occurences. I reckon that must be reminder text for one of the new keywords. WUBRG - 0. No 5-colour love here. Also 0 for 1WUBRG thru 5WUBRG as well as WWUUBBRRGG, and the three- and four-colour combinations. And yet, Nephilim - 2 (!!) 3WB - 1 (known) WB - 1 } UR - 1 } Anyone care to analyse implications for split cards? 3UR - 1 } 1RG - 1 } 3RG - 1 UB - 2 } RW - 1 } 3RW - 1 1GW - 1 XGW - 1 XBG - 1 (known) 3BG - 1 // - 20 (it's used twice in the text of each split card - once in the name, once to separate the rules texts)
Lyzolda, the Blood Witch (Wizards spoiler, but not on magicthegathering.com) 
(includes full text of one not-yet-officially-spoiled card) Fair enough, so she is. She's an officially-leaked card. I'm still not sure how that stands with the usual purpose of this page, especially considering that article also spoils at least one other card in the text. --CH (who opted not to read said card just in time, so now merely knows the name of the Rakdos mechanic)
Sorry, I didn't actually read the article. That's a bit naughty of them... --qqzm
She is an extremely cool card, however. One I can see getting more tournament play than any of the guild champions in Rav or Dis, too: aggressively costed and with a very nice ability. --AC
Accessible via the [Dissension minisite] is an Azorius "Special Art Preview". If you solve the jigsaw puzzle, you get a funky wallpaper and the card name "Windreaver". It's funky, funky art, and makes me really quite eager to see what the card does. Yes, yes I am allowing myself to be hyped by slow teasers. What about it? :) --AC
Given that you can click the 'solve' button to solve the puzzle, it's not all that hard to get. --Angoel
''It's also Azorius-aligned. Note the watermark on the wallpaper.
Well, given it's linked from the Azorius minisite... ;) --AC
Also included are brief hints as to the mechanics:
Rakdos - Hellbent. Encouraging risky sacrifices for both short- and long-term gains. "by far the most adrenaline pumping strategy of the ten guilds. It's inconsistent, but when it works, watch out."
Simic - Graft. It allows creatures to enhance other creaures, and involves +1/+1 counters. That's all we know.
Azorius - Forecast. A controlly mechanic that can nevertheless turn into an quick win once you've gained control. With a name like "Forecast", it surely must have some aspect of looking ahead. "It can be played to slowly and methodically gain advantage inch by inch, and in the late game, it can simply be used to win. ... sit back and monitor the game, stepping in where you see fit to make sure that things go your way."
This is an intriguing hint. I can't really think of what this could be. The first half makes me think of card-drawing, but how could that be used to win? Unless... How about selective milling, being able to repeatedly look at the top card of your opponent's library? I know that was Dimir's win condition, but you could use MTG: Wizened Snitches in a Azorius deck just as well as in a Dimir deck. Although the MTG: Lurking Informant has precisely this flavour and he's clearly Dimir. --AC
I know this would be heinously powerful, and steps on the toes of the Dimir a little, but how about an ability to play cards straight out of the library? --CH
In discussion with AlanLawrence last night, he proposed manipulating your own library in MTG: Information Dealer style, which feels more blue and less black. This at least seems extremely consistent with Aethermage's Touch, below.
On a related note, I've been musing about what the Azorius' stereotypical win condition will be. When Ravnica came out, we were told that each of the guilds had its own mechanical way of winning. Boros swarm, Gruul stomp, Rakdos charge suicidally. Selesnya accumulate hordes of creatures, Golgari and Simic prefer to build up a few big creatures in (I suspect) rather different ways. Izzet win with instants or sorceries, Orzhov bleed, Dimir mill... so what's left for the Azorius? I propose that they could be the "alternate win condition" guild - as in, they have several cards that provide a condition for winning, like MTG: Celestial Convergence or MTG: Battle of Wits. This would be (a) really really cool, (b) very different to the other guilds, and (c) perfectly in flavour for the guild who make the laws that all other guilds have to follow. Naturally, they'll have other ways of winning too, just like the other guilds have some ways of winning outside of their primary stereotypical way - Dimir and Orzhov have evasive creatures, Selesnya can do big creatures, Golgari can do saprolings, Boros can do control, and so on.
If this is the case, how could it interact with their keyword mechanic "forecast"? Well, it doesn't have to interact directly - Haunt is nothing to do with bleeding, for example, and Transmute only tangentially relates to milling. "Forecast" could be a way to find one of your relatively few win condition cards from your library. --AC
That would be so freakin' cool! I hope you're right... --CH
It is amusing, but I don't think it works. If you play the Dragon first (and float mana for Rakdos or something), then you'll have to sac the Dragon as soon as you attack. If you play the Dragon second, it'll just eat the Demon along with everything else. --AC
Yes, the point is either to drop a land as well as Rakdos, in which case you can just sac the land; or (and here's where it gets really silly) actually intend to sac the dragon with Rakdos. You just got a free attack from him. Granted, you've also sacrificed a 7-mana flying dragon... --CH
It reminds me rather irresistably of [Vanish into Memory]. I'm not sure quite why, other than the whole "2WU rare instant" factor. I think it's the "move a creature between different zones at instant speed, and set up a delayed trigger to move it again in a little while" factor. --AC
Wow, Johnnilicious! I have at least 2 decks already that want one, and that's without having any GU decks or having built anything containing Simic cards yet! I think I'm going to happily trade for as many of these as I can physically get my hands on. They have a diversity of uses that won't run out, I feel. A very viable contender for Johnniest of the Guildmages, competing with the current reigning champion MTG: Izzet Guildmage. (And, as ChMi? points out, the interaction with MTG: Bramble Elemental is truly frightening.) --AC
I just realised I'm a little hazy on rules here: "Attach target aura enchanting a permanent you control to another permanent you control." Does the second perm have to be a viable attachee for the Aura, or can you get rid of a nasty MTG: Pillory Of The Sleepless by attaching it to, say, a Forest and watching it fall off? --CH
212.4e An Aura spell requires a target, which is restricted by its enchant ability. Other restrictions can limit what a permanent can be enchanted by. If an Aura is coming into play by any other means than being played and the effect putting it into play doesn't specify what it will enchant, the player putting it into play chooses a permanent for it to enchant as it comes into play. The player must choose a legal permanent according to the Aura's enchant ability. If no legal permanent is available, the Aura remains in the zone from which it attempted to move instead of coming into play. The same rule applies to moving an Aura from one permanent to another: The permanent to which the Aura is to be moved must be able to be enchanted by it. If it isn't legal, the Aura doesn't move.
And now we know Forecast. Basically, "Once per upkeep, you can reveal this card from hand for Mana and get its effect". Could be powerful, and I reckon is rather nice in Limited. Although not against Terry Soh... --CH
Indeed. Forecast is an intriguing mechanic. I don't know how closely the Forecast abilities will necessarily match up with the card's abilities (I'm avoiding unofficial spoilers this time round), but I can see why it got its name. You have to predict whether you're going to want that mana for something else, as well as giving your opponent a forecast of things to come. It's interesting that, like the Rakdos Augermage, it's useful whether you're the beatdown or the control: plenty of aggro WU flying decks would love this card for its inherent ability. --AC
I love "Odds". That's a brilliant card. Also, MaRo reveals the rarities - 5 enemy pairs at rare, 5 allies at uncommon. --CH
Yay! I was hoping they'd do some uncommons, but not really believing it'd happen! And Odds is a superb card indeed. Imagine it on an MTG: Eye of the Storm... (In fact, if split cards went on the Eye, you get to choose which half to play each time. Ibble.) --AC
It could really mess up some decks nastily, and it's tricky to get rid of. I can't help wondering whether it will be used mostly as countermagic or token-generation. --Edwin It's pretty, too. I like the Azorius Hybrid frame. --CH
Indeed. I love the way AA told it - such that you could figure it out almost completely by the time he revealed it; and that he managed to include combos and tactical discussion, all in-character. I'm impressed with the rare hybrids here - it's looking like 9 out of the 10 are going to be cool. MTG: Master Warcraft and MTG: Shadow of Doubt are inherently narrower and more restricted as one-offs, and I still hate the MTG: Giant Solifuge, but all the others are really rather funky. If the Simic's one is equally cool, then WotC are to be congratulated on a 90% hit rate. --AC
A few fun things occurred to me to combo this with. Firstly, as AA points out, it's a bit insane with MTG: Pride of the Clouds. If you want your spells to do something, you can always go for the Storm spells from Scourge - the main spell will be countered and get birds, but the copies weren't "played", so they'll resolve. MTG: Mind's Desire would be particularly fun; but taking that to its (il)logical conclusion, I think the award for "most insane counterpart" has to go to MTG: Eye of the Storm. --CH
Am I right in thinking that with MTG: Eye of the Storm, you can stack the triggers so that the card you play that gets sucked into the eye produces birds on the way into the eye, and again when you play the copy? --Edwin
I think you might be, although the Eye would produce birds first. You put the Dovescape trigger on the stack followed by the Eye trigger. Once the Eye's finished, the Dovescape trigger still exists. It isn't targetting anything so it won't fizzle... In fact, you'd have to do it like that, or the spell would be countered before the Eye got hold of it. --CH