I don't really know why you bring up Sakurai - this is Project M we're talking about, not Smash 4, remember?
Ya sorry I get carried away sometimes, I'm on more than one forum so ya... And I went to Sakurai cause we already know Geno can't be in P:M
Just to respond to it, though - Sakurai is catering to the masses (as he should for a game of Smash's scope), and the masses mostly haven't heard of Geno (as tons of them started gaming well after Mario RPG first appeared) - not to mention, there's much better surprise characters to be picked, even among Nintendo's own property.
I don't know if he's catering to the masses. He doesn't always... He always picks random characters no one wants/thinks to want. PLUS he has said he won't be listening to the fans this time around (such is my understanding).
When it boils down to it, Geno has only been important in a single game - one that has been mentioned only once after it's release (with him appearing in that mini-game in Mario & Luigi). I could change a few words around to make something comparable:
Also I would argue that other than Mario himself, Kersti was THE most important part of Paper Mario Sticker Star. She was the mysterious character specifically opposing the antagonist (Bowser) and guiding Mario along the way.
Of course, it's more complicated than this, but it's a simple example; Geno's absolutely not important enough to take the fifth Mario spot as well as one of the limited third party slots.
ROB has been in 0 important games. Pit and Ice Climbers pretty much only one or two important games and became irrelevant until being re introduced in smash. I think Geno could EASILY get similar benefits from being added. Even the likes of you might gain some respect for him if you get to play as him. He's a very minor character, but at the same time he is this really mysterious, interesting character that I feel could use some more spotlight. Its not the characters fault he hasn't been seen since SMRPG. He could be given his own RPG and it could turn out awesome! We don't know. I also had no idea he showed up in any other game after SMRPG.. that even increases my hope more lol. I do see why you would hate him BECAUSE of the annoying fan boys, but I think if you give it a chance you could become a bit more open to him.