Wow, you did it! XD
These are nice and well thought-out for the most part. The only one that I feel is more likely than you think is Ryu Hayabusa. I get that he's been speculated a lot mainly because of some of the more famous leaks that have come out, but I honestly think that Nintendo and Koei Tecmo's working relationship has been too good over the last several years for it to not lead to Ryu coming to Smash Ultimate. Just think, Koei Tecmo has helped Nintendo develop Hyrule Warriors, Fire Emblem Warriors, Marvel Ultimate Alliance 3, Fire Emblem: Three Houses and Hyrule Warriors: Age of Calamity, they've ported several other games from the Warriors and Atelier series to the Switch, The 2 co-own the Fatal Frame series, which is already represented in Smash Ultimate with Yuri Kozukata as an Assist Trophy and a few spirits, and the classic Ninja Gaiden games are considered by many people retro 3rd-Party Nintendo classics alongside Mega Man and Castlevania (both of which now have playable representation in Smash). Not to mention the leaked Ninja Gaiden Sigma Trilogy for Switch/PS4 supposedly coming in March, which is around the time that Challenger 9 is likely to be revealed.
As far as other Koei Tecmo characters go, Ryza's already been disconfirmed, a Warriors, Nioh or Fatal Frame rep seems unlikely, and Kasumi... well, despite Yohei Shimbori (The Diector of Dead or Alive 5 and 6) saying in a foreign interview that he would prefer Kasumi being in Smash Ultimate (as would myself honestly), the whole "Smash is for good boys and girls" joke kinda prevents her inclusion... I mean, unless they go with her DOA5 Night Sakura outfit. Ryu though, is just too iconic a character to not be the Koei Tecmo representative of Smash Ultimate's roster. Plus, because of the relationship bewteen Nintendo and Koei Tecmo, Ryu could be the Terry of Fighter Pass 2 and come with a ton of music from Ninja Gaiden (both classic and modern), Dead or Alive, and Fatal Frame (Though this isn't guaranteed, I suppose).