I know that this discussion was from pages back, but Bowser and Ridley are very different characters.
Bowser comes from a more magical universe, and he is himself supposed to be a powerful sorcerer (though apparently not a very good short-term combat sorcerer). So not only is Bowser's size very inconsistent across games, but it can also be explained in a hand-wavy way. It also has little impact on his character overall as long as he's bigger than Mario, judging by the fact that he occasionally feels the need to make himself even bigger.
Ridley, on the other hand, has towered over Samus in every game other than his NES incarnation. Where Nintendo fails to convince people that Bowser's consistently at, say, the size he is in Super Mario World or Super Mario Galaxy or New Super Mario Bros. Wii, the Metroid games are quite consistent in depicting Ridley as a Godzilla-like figure that Samus encounters over and over again, once they have the hardware to do it (i.e. not the NES). The precise size does not come into the picture in either Bowser's or Ridley's case; Ridley is supposed to be really fucking huge.
If indeed the guys at Sora aren't thinking about the size issue as much as we do, then my bets are highly against Ridley ever becoming a PC. It just wouldn't "feel right" for the reasons I've given. That's why he got the same treatment in Brawl as, say, Rayquaza.
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As for the Tales suggestion, I kind of have to agree that it would be difficult to separate a Tales character from other Smash sword fighters, unless said character had something different going for him/her. In this regard, Cress/Cless seems like the only protagonist who could really fit that bill, mostly due to his spacetime hax powers. Other characters usually have to resort to Mystic Artes to do similar things. Even that seems rather inadequate, though. Still, I'd kind of like to have him in Smash just to see the awkwardness when old and new fans clash over how his name is spelled :P