I just found the Spirit's grade really odd, but maybe I'm reading too much into it. Also,
KirbyWorshipper2465 did point out something I had forgotten - that his friends went AWOL (Globox did have a trophy in 4, IMO he and the Teensies should have Spirits at least) so that's part of the equation.
Still, I don't think that the Rayman / Ezio situation is that comparable with the Banjo / Steve one. Also, fan demand does play a major role, but I'm a bit skeptical as to how much. Especially when Joker started the Pass, and the currently most speculated character is Doomguy. Neither have been really highly speculated until pretty much recently. Even allowing for the Hero to be fan demand (which is reasonable), that's 2 out of 4 characters if Doomguy gets into the game.
Sakurai / Nintendo would likely spread out characters from different genres / character types, but genres depend on how Sakurai / Nintendo define them. For example, does Banjo-Kazooie count as a Western platformer, or collectathon in their minds? If it's the former it could hurt Rayman's chances this pass, if it's the latter it could help. Likewise with Ezio: Is he a bit too similar to Joker as a character type in Nintendo's minds (with Joker being a stealthy thief and all, not far removed from Ezio's Assassin style)?
I find it decently likely that Ubisoft and Nintendo have talked about a playable rep since 4, but hit a bit of a wall / impasse. Could be something seemingly ridicolous, like Sakurai having trouble with Rayman's moveset or whatever.