If they want to cash in on Ridley as a character they might want to avoid having him represent a game that was beaten to death by critics and fans alike.
I've always thought it was a bit odd to have characters represent their latest appearances, I know it works well at selling the most recent games, but I think that the characters should have their most iconic looks, which I'm sure that Fox, Falco and Wolf will get back with the Star Fox 64 3D remake.
They did it right by not giving Samus the Prime look (the Prime look is a seperate trophy all together,) and even if Zero Mission was new enough to keep that as an excuse, it was solely based on her Super Metroid look, given that Samus never has her classic orange Power Suit in Zero Mission, she only gets the big shoulders when she gets the Gravity Suit in that game. Plus, I think it was at Gamescon '07 where a representive literally said they had based her on her Super Metroid appearance. It's also supported by the fact that every other Metroid thing in-game was based on Super Metroid, Ridley too.
Plus, if Retro Studio's new game that "everyone wants us to make" is a Metroid game, which seems pretty unavoidable right now, they could always use the upcoming designs, because no way can a new Ridley design be as bad as the Other M one where he looked like an overgrown chicken (which was essentially what he was I guess.)