As speculated, Oni and Evil Ryu have been revealed for Super Street Fighter IV Arcade Edition and are fully playable characters! Originally assumed to simply be bosses for players of the arcade version, these two new characters have their own unique move-sets and Ultras.
Oni appears to be similar to Shin Akuma, with the standard Shoto character's special attacks (Shoryuken, Hadouken, etc) but with a few new twists. He looks to have an air-hop/air-dash, a cross-up slash which can be combo'ed in and out of, among others. His Aerial fireball Ultra has also been shown and looks like Akuma's Messatsu Gou Hadou from Street Fighter III, with players able to use it either when grounded or whilst jumping.
Evil Ryu also makes his appearance in Arcade addition with a few new tricks, including a couple more overheads than usual and a new Focus Attack. His Ultras are new, but in similar fashion to standard Ryu's U1/U2 in that they can be used as part of a combo. He's currently looking the stronger of the two characters, with all of Ryu's old basic combos working fine and a variety of new tricks up his sleeve.
Check after the break for video footage of each character in action!
Warning: Some of the language used in the following videos may be deemed unsuitable for children.