Check my latest post in the Arizona vs. VSM thread...I talk about this a bit there. I've wanted to post about this for awhile now so this is perfect!
So based on the upcoming release schedule, the way Evo tends to pick games, etc., I think at this point there are four games that look like stone cold locks for Evo next year:
SSF4AE 2012: Shouldn't need any explanation.
UMvC3: See above.
Street Fighter x Tekken: It's going to be the "hot new thing" from Capcom at this time, and Evo has always been a Capcom-focused tournament. If Tatsunoko vs. Capcom could get into Evo, this should be a no-brainer.
Soul Calibur V: Evo needs a Namco game - they've always had at least one since 2003, T6 is dead, TTT2 won't be out on console in time, and the SC series has a pretty decent history with Evo. FWIW, Namco is also one of the biggest sponsors at Evo, although I can't say exactly how much that factors into game choices if at all.
Now, I highly doubt Evo's going to only have 4 games next year, so let's look at the other feasible candidates:
Mortal Kombat 9: Highest Evo turnout of any game ever besides SF4 & MvC3, fantastic top 8, biggest mainstream presence of any FG besides SF4, yadda yadda yadda. Seems to have less of a consistent tourney presence on the west coast and in Canada than elsewhere. Like STORMS mentioned, there are a lot of strong international players emerging, so there is plenty of potential for improvement over this year's tournament if it gets back in. However, there is a perception among the wider FGC that MK is dying, and the lack of a 100+ player tournament since Evo only fuels that.
Blazblue CS: Extend: Blazblue this year had its best possible situation - the newest version had come out on console fairly recently, and it was a clear improvement over the previous games. And even with all of that, it still had less than half the turnout of MK. Its numbers were about the same as Tekken 6's, and it didn't have the excuse of being an old dead game like T6 did. BB also consistently draws lower turnouts than MK at other majors and regionals, and certainly much less stream hype (though Evo top 8 was really good). Add all of this to a new version that will be unproven compared to MK9, and I think it's a weaker candidate by just about any standard.
Skullgirls: I think this is the big wild card. No built-in fanbase (besides Mike Z's fans on Dustloop, lol), but it's generated some good buzz and received a ton of coverage on the SRK and TYM front pages. Its visual style seems to turn off a lot of people, and I could see that hurting sales and perception. Being cheaper than the other relevant FGs should help, though. GGPO is by far the best netcode there is, so it should draw a lot of attention from serious players on that alone...but many casual players don't understand GGPO's benefits and get confused by the rollbacks. It also won't be out until next year, but that could be a positive as far as hype goes. And its creator is a player with major roots in the community and friends among some of the higher-ups in the scene.
At worst this game should be big among the anime crowd, so I think the Blazblue numbers from last year represent its floor. As for its ceiling, who knows - Capcom players frustrated with their games could get drawn into it by GGPO and end up enjoying it, and in particular I could see some MvC2 & Guilty Gear specialists getting into this since it plays more like those games than MvC3 and Blazblue do. Alternately, everybody outside of animeworld could not give a shit and continue bitching about Capcom games while playing them anyway. It's really hard to say, but this game shouldn't be a total flop at least. And given that Evo likes to feature fresh & new games and has been willing to take chances on much riskier stuff in the past (e.g. DOA4, Mario Kart DS, hell even MK9!), I would say this looks like MK's stiffest competition.
The King of Fighters XIII: This looks like the least likely of the new games. SNK has just never had much of a scene in the US - even MK in the dark days was probably bigger. It's also highly likely that people will be scared off by how awful KOF12 was. If it uses GGPO, then I could maybe see it picking up a following here, but I recall hearing that isn't happening. It's a shame, since I think this is perhaps the best of the current crop of FGs, but it's hard for me to imagine how it would draw even 200 players at Evo. In short, KOF will probably continue to be the soccer of FGs.
So, to boil it all down, I think MK will be safe if Evo decides to go back to 6 games next year. If they stay at 5, I think it will still be a front-runner but far from guaranteed. As I mentioned in my other post, we really need to finish this year strong at majors if we want to make a good case. Evo tends to decide on the game lineup pretty early in the year, so we need to rep well at Devastation/Season's Beatings/NEC to prove that we still belong. Even Winter Brawl and Final Round may be too late, though I don't remember exactly when they decide on the games.