I just think that we are gonna be getting Ryza instead, and Ryu Hayabusa will be just a Mii Fighter costume.
While there are many Koei-Tecmo reps possible, the fact that an Atelier character would
literally have the same crafting mechanic as Steve is a giant blow to the series' chances. Shame because it is a cute series with great music and I thoroughly enjoy Ryza.
With that said, KT also has:
Dynasty Warriors/Hyrule Warriors - Their biggest series and has a Nintendo-specific spinoff with beloved characters from a popular IP in Zelda. Someone like Lu Bu would bring unusual and interesting mechanics to Smash.
Dead or Alive - A popular 3D fighting game that is still getting new games. Kasumi has a possible shot.
Nioh - Recent hit, and getting a sequel. Outside shot, but worth mentioning.
Fatal Frame - Maiden of Black Water got an AT and spirits and was a Nintendo game. We don't have a horror franchise in Smash. If Monster Hunter is back in the mix, so is Fatal Frame.
There is of course Ninja Gaiden and Ryu Hayabusa, and honestly after seeing Steve I think Hayabusa would be awesome - imagine the million-IQ plays we could see from a Steve vs. Hayabusa match, with Hayabusa able to scale the block walls!