I dunno... Sora's one of those guys that casuals love, but will be likely violently rejected amongst hardcore fans. My issues with him (and this is regarding his liklihood of being a DLC fighter and not 3rdPartyArts) is that he's a third-party character that hangs out with Disney IPs. But anybody who wants Geno and hopes Nintendo asks SquareEnix for him will likely see Square suggesting either Sora or Cloud Strife, both are terrible choices, especially since Cloud was featured in the first game Squaresoft made after ditching Nintendo for Sony and the PlayStation, and no version of FF VII has ever been on a Nintendo console. As much as I made arguments against a Ryu over on the Rayman support thread, at least Ryu makes some sense since he appeared on quite a few Nintendo consoles (though there was a long gap between the SNES games and Street Fighter IV as a 3DS launch title).
Sorry for not discussing Isaac, but we kinda need to let our opinions about certain things be discussed while talking about Isaac.
EDIT: Also just looked at the DLC for August, and from what I've read, those stages are Wii U only... certainly the 3DS won't be shortchanged in the DLC department, hopefully.