2D games like KOF, Fatal Fury were still feasible to be in a good crossover game with SF and there you go, you got CVS, and then, I still believe Namco should have done this with SEGA instead to give more pump to the VF series and make a more sense crossover true.
True, it would have been really awesome of capcom to help give VF some more exposure. Personally though, I think DoA is closer to Tekken's style than VF is (though I haven't played VF since the PS2). If it was Tekken X "another 3d fighter" it'd just be a matter of the button layout to change, like what happened with CvS/SvC. It's strange, but I didn't think of it till now... SF has always been a 2D fighter, and people rarely (if ever) dreamed of a 2d fighter crossing with a 3D, since it seemed obvious how the two wouldn't fit. It's because SF is all 3D models now that it doesn't seem as odd anymore, it feels like a trick of the mind. If SF4 had stuck to complete 2D this day wouldn't have come. In fact, it's even wierder to think how SF characters would fit into Tekken's gameplay than the other way around, it's going to be interesting to see.
As for the special moves of Tekken characters, I've always considered some Tekken characters to have "special moves", like Kazuya's up+forward RK,RK,RK (jump, QCB + K), or back LP + RK (maybe HCB + P), and devil jin has ones you can guess. It'd be pretty easy thinking up a movelist for Tekken characters if they were SF characters. A nina (or many other Tekken char's) kick combo could be like Kyo's aragami chain (but with K). Though, I'm just assuming that's the approche Capcom took with the Tekken folk.
I guess you have to look at the game kinda "mugen" like. It'd be interesting to try, at least just to see how all the Tekken characters feel in this style.