Images of Xbox 360 achievement icons for Super Street Fighter IV may imply that the game has a couple of new challengers incoming, including Evil Ryu, Oni Akuma and Yun and Yang.
The achievement with Evil Ryu is titled The Awakening and you'll have to beat arcade mode on the hardest difficulty. Birth of the Oni depicts Oni Akuma whom you have to beat on the hardest difficulty in arcade mode.
They have yet to be officially confirmed so take it with a pinch of salt. More images and descriptions through the source.