Well, it's possible, maybe not the best but still possible. Remember KoF2k1 and its striker system? I'm thinking that if it only has exactly 4 buttons that it could work like that.
...But...people hated 2K1 for a lot of things...among them being that final straw that made it so nobody wanted anything more to do with the "Striker" system.
Besides, if there's one thing I'm sure people hate, it's the notion of trying to map too many things to groupings of buttons, or trying to map too many things to a single button. It's one thing to hit two buttons for the sake of activating a Hyper Combo, or some other type of system specific function. It's another thing altogether when you start getting a bit ornery with it, which is what I think would happen if they tried to do some sort of bastardized fusion of TvC and/or KOF01 did it with the Assists.
I mean, I already wasn't that hot with the idea of how you had to press BACK+ASST in order to tag out manually in TvC, because it reminded me a bit too much of KOF01. So many times I had to fight with that mechanic, that I often just said "screw it" and focused on using the DHCs and Aerial Variable Raves as a more reliable means of tagging out. While it's a good strategy altogether, I really don't want to have to face that kind of that crap again, only with whole nother button to be concerned with this time. No thanks. I would have rather had my LK+LP/HK+HP means of tagging out.
And let's forget how TvC was pretty ornery when it came to doing Crossover Hyper Combos, too. You had to execute the super and THEN press the tag button within a certain amount of frames to get it off. No previous game in the "Marvel" style forced you to do THAT much work in order to get off a Crossover Combo.
It's things like this that just serve to boggle my mind when it came to TvC. They obviously wanted to make it a much more casual affair, and yet they did a number of things that I think were not conducive to making sure the user never had to worry about "fighting the controls" in order to get off basic things that were easy enough to do in past games. Hopefully, Niitsuma has heard the various remarks relating to TvC, and won't allow such things to happen all over again in MvC3.