Since there seems to be some major misconceptions going on here...
This is Capcom's take on a SF Tekken crossover game, based in part on Ono's (the producer of the modern SF series) love of Tekken Tag Tournament. It uses a modified version of the SF4 engine but, as is obvious, it includes a much more full juggle system than SF4 did. Beyond that it supposedly plays much like a hyper version of SF4 but with some Vs game style elements added in.
Contrary to popular belief, the Tekken characters are not really being totally shoehorned into a SF control scheme. The Tekken characters use the left 4 buttons of the 6 button layout just like you do in Tekken with it's 4 button layout. The 2 rightmost buttons (hard kick and hard punch generally) will be used as sort of special move buttons for the Tekken cast. They will also have some special moves akin to what the SF characters have, and these are based on some of their moves from the Tekken series, but they will be able to access at least some of their normal Tekken chains via the same inputs on the 4 attack buttons just as if you are playing Tekken. From early reports, it also sounds like the Tekken cast are being created to take better advantage of the new juggle engine than the SF cast are, which fits perfectly if you know anything about Tekken.
Namco is making their own version of a crossover game that features SF characters in a more Tekken like system. You haven't seen much of it yet because it's quite early in development.. much earlier than SFxT. And yes, it will be called Tekken X Street Fighter. No real details are known as of yet as to fairly important things like how Street Fighters famous projectiles will be implemented in a 3D game.
