I don't quite have the memories of Metroid most you guys do. I had the original game and the first Prime game, neither of which stuck with me in the long run (despite the latter being considered absolutely amazing, I never finished it - but I still have it).
I was really impressed with Ridley in Brawl. I don't know if that's a popular opinion with you guys here, but I liked both his boss fights quite a lot. If he's anything like that as a boss in Pyrosphere, I don't think I'd complain much either. He feels a lot more like a boss fight to me than a playable character, but this is based on the way he's been presented to my knowledge and recollection of the character. He is a big scary purple space dragon thing, to me, who thrives on the intimidation of his size and mobility to hunt you down as you try to plink away at him for your life.
That said, if anyone can translate that into something fun for people to play both as and against, it's Sakurai. He's really impressed me with a lot of the newcomer playstyles as seen so far, and I'm sure he could work that same magic on Ridley if he makes it in the playable roster.
I'm totally certain he could make something great off the concept of a really large character, even bigger than Bowser - assuming that he would be huge as a playable dude, anyway (and I feel he ought to, to best convey what I get of his general character - not as big as in Brawl but still huge).
That and I guess I'd enjoy putting him in bunny ears and having him wave around some little fairy girl's flower wand, because that's just funny.
Even if he doesn't make it in as playable, I'm certain what we will see of him will be well done, finely polished, and fun to interact with. He is a major element of the Metroid games, that much is clear, and that will be absolutely acknowledged in some form or another.
Sakurai's had to balance a lot of ideas and IPs across a very big team, on two different projects, nonstop. He's done bad things to his shoulders just to get this all put together. I'm sure his team will do everyone justice to the extent that their time, resources, and physical health allows them.
Regardless of the end result for Ridley's representation in Smash, I can't wait for the game's release in Japan - or the local release here some weeks later.
It's only sad we'll have to wait many years again for any further speculation of this nature, haha.