Well, some new info has been given if you go to Gamespot. They have an interview up there that explains a little bit more about their reasons for going for this crossover. In the interview he confirms that fatalities WILL be in the game, but for all the MK characters and DC villains only. The DC heroes will have non-lethal "finishing moves" or brutalities. He also mentions that no one has been able to guess the character roster correctly, but the ones that thought of parallels between the MK and DC characters were the ones who came the closest.
Another article I read mentions that an interview with someone from Midway revealed that he's 100% certain Shao Kahn and Darkseid are in the game (and when you think about it they're parallel to each other).
http://www.the-nextlevel.com/board/showthread.php?p=1064137869#post1064137869
As for Midway's decision to do this crossover, in my opinion while I'm skeptical about it in some ways, it could be an great side franchise for both MK and DC. DC has had horrible luck in the videogame industry as none of their games have even cracked the top ten lists out there, and MK has needed something to spark up the series. Capcom and Marvel had a great alliance for awhile, and the games were awesome. And when you think about it, the lessened gore is a good step toward focusing on better gameplay rather than blood and effects.
Look at MK: Shaolin Monks for instance, yes it wasn't a dead on fighter, more of an action adventure game......but because Midway's main focus was finally on the gameplay, they managed to make a great game with blood and fatalities. Now I imagine they're at least trying to make the gameplay fairly great to make up for the less brutal fatalities, which thankfully will still be in to appease the fans. So I expect this to be a sleeper hit, and will make the hype for MK8 that much greater.