Katsuhiro Harada recently answered a question on his Twitter Feed which clarified a statement he made a while back about the upcoming Tekken X Street Fighter. He said that only Street Fighter characters would play with six buttons in Tekken X Street Fighter. Tekken characters, on the other hand, would still control with four. Combined with his previous statement that Street Fighter characters might use some sort of resource meter while Tekken characters would not, it sounds like they will play completely differently than the Tekken side of the cast.
Source: Harada’s Twitter