I'm sure a lot of Marvel's stuff is done to tie into whatever they're trying to promote in print or film. Thor and Captain America have movies coming out soon, apparently X-23 is getting her own solo miniseries and that's why Marvel wanted her in, and so on.
As far as alternate costumes go, I just hope there's a classic Bionic Commando skin for Spencer instead of the reboot version. Bonus points if it's the one from Rearmed 2 with the awesome 70s mustache.
Also, from various panels and streams people managed to get a few more deconfirmations out of Niitsuma: Gambit, Silver Surfer and Squirrel Girl are all apparently out. I know some comic book enthusiasts were really hoping for the latter to be MvC3's Servbot.