Well in the new character thread a lot was said.
The biggest thing is everyone wants him, but every designer knows that for something to be worth doing the player has to react positively to it. If the character model is brought down (which is why sakurai won't use him: he's too big) a lot of players wouldn't feel they were playing ridley but a different charizard or something. Also there are no incredibly huge characters in brawl already (I mean like by design huge, similar to great apes in every dbz game), so it would bring up the question: who else should be big?
It's not like the community doesn't realize that metroid is pretty poorly represented, and the other metroid character who was also highly voted was dark samus. She would be much easier to design, and it's not like she was a ton less popular in the votes.
I don't think Ridley should become a thing, that Ridley character you tried was designed to be big. That's fine. In a competitive game like project m having one big character throws off balance for that character and you just get the heavy vs. fast debate on a larger scale since his hitbox is so damn big.
tl;dr I think not, but it's not impossible.
