What do you think about the idea of Outer, Player's Character in Daemon X Machina, being the last DLC character? It would make some sense. Daemon X Machina's release window is just 2019 right now, so the last fighter being early 2020 means that it would be months after the game's release and I'm sure MARVELOUS would work with the Smash team before launch. It would make sense from Nintendo's point of view, just like with Bayo they're promoting an exclusive that might have more installments in the future.
I don't think as a fighter the Outer would be in their Arsenal (their Mech) , as I'm pretty sure it's actually too big. From my measurements, it's about 3.5 times the size of the Outer, who is superhuman, so they're probably either simmilar size to the other human characters in smash or taller. I'm researching a potential moveset for them rn, might do a seperate post about that.