Check out J.R.'s Akuma playthrough of Arcade mode in SFxT, at 20:00 you see Akuma’s ending cinematic… and we see Oni!
Is there some small, wonderful chance that we might actually get ONI in this game? I will be so ridiculously happy if he actually ends up being playable… I was sure that there was zero chance that he would be, but this gives me a bit of hope 
Sorry, he ain’t in. The DLC characters are going to be Sakura, Blanka, Cody, Guy, Elena and Dudley for the SF side and Lars, Alisa, Bryan, Jack, Lei and Christie for the Tekken side. =(
Who knows if they’ll add even more DLC characters, but I seriously doubt it.
You can see the top and bottom line is the boss line (Or I think like that). I think they can add Oni, Evil Ryu for SF and Azazel, Devil Jin for Tekken
I think Oni style is fit with this game well
Let’s hope
btw, In the ending we can see Oni is just as small as Akuma. Hope if he appears in game Capcom will reduce his hurbox