It has to be a separate mode, there's no way there were gonna through with that. If it was the default mode you would only see very few characters rotating.
Vanilla Sagat, Akuma, Ryu, Rufus, Seth, Viper
Super Cammy, Bison, Adon, Chun, Abel
AE Yun, Fei, Yang, Makoto
In a sense almost everyone else is gonna be obsolete.. there's a REASON why these characters were patched and adjusted for 4 different versions, and no bringing them all back at once for a massive clusterfuck is not that reason lol.
Just imagine Vanilla Akuma vs Hugo, dude wont even get to move <__>