I'd really like it if they kept it pseudo-3D (as in a 2D fighter with 3D graphics). I know I'll be disappointed with anything other than DOA. Nobody has quite gotten 3D fighting perfect yet... especially since collision detection is so terrible in alot of fighting games. I'd love to see maybe "restricted 3D" KI3; where the character movement is limited to 2 dimensions as a result of the environment.
Until someone gets collision detection right (if I punch someone in the foot while their jumping... it better not start a damn combo) I'll just keep my DOA and dough.