About Ridley, if I may;
I honestly do not think that what Sakurai says about Ridley is him saying it can't happen at all in regards to him being in Smash. What I think is the issue Sakurai has with Ridley is the way he tends to be used in Metroid making it much harder for Sakurai to find a way to work around his size to represent another aspect of the character like with some other bigger characters.
Think about this; what does Ridley tend to do in his fights? Fly around or into you, spit fire at you, grab you and scrape you around, maybe slash with his claws and tail. He's got some moves to work with, but there's not a lot of material to use to make a coherent moveset that feels just as Ridley should feel, and the fact that most of his interesting characterization is from a somewhat obscure manga doesn't help. Making him a boss makes it so they can use the moves he does use most often without having to come up with a lot of other things that still feel like him as a character. His moves in the games don't neccesarily line up with the sadistic, genocidal horror that the manga depicts him as, which creates something of a disconnect.
Sakurai's an artist who needs some frame of reference to make his art, and in terms of the Metroid series, Ridley hasn't really been given any of his manga characterization and his fights tend to be pretty samey, which are pretty painful points against him. I imagine if Ridley is given a boss fight that properly represents his character (say, giving him more feline and bird in the fighting style), he'd be an easy addition for Sakurai to do, because then there's a lot more material to use for crafting moves.
Sakurai knows Ridley is highly-requested, but the lack of reference material in the games is what's hindering Ridley's progress as a fighter.