This is a scary thought but I think Ryu Hayabusa is going to be a Mii costume in Smash rather than being an actual character just like Travis Touchdown and Dante. I mean, the Mii Swordfighter already has a shuriken side special lol. I would be shocked if we didn't get any Ninja Gaiden representation in Smash tho.
1) TMNT in Injustice 2 (even though I didn't play and I probably won't play the game, the trailer was quite surprising)
2) Mai Shiranui in DOA5 and 6
3) Akuma in Tekken 7, in which for some reason Bamco/Harada decided to make him a story relevant guest character