Ok, since obviously no one knows much about Geno, I (having loved the character since his arrival/departure on Super Mario RPG) will give a quick little background.
He appears, as afore mentioned, in SMRPG, which is a game for the SNES by Nintendo (and this is the important/controversial part) with help from Square. His rights are technically owned by Square (as reveals McFox's email to Nintendo concerning the matter a while back), meaning that he'd have to come in as a 3rd party character.
Even though owned by Square, he has appeared as a cameo in at least one other Mario game, specifically the Mario RPG for the GBA (I can't remember the name...it's late, haha). He didn't do much of anything, except state the rules for the minigame he was cameod in.
So, there you have it: Geno is owned by Square, which makes him OFFICIALLY a 3rd party character. Everyone needs to get that.
Reasons why I think he's a great choice:
~He's got that Smash feel about him, just like Ness and the Ice Climbers do.
~He's a retro character, which Sakurai is obviously taking an interest in.
~He's the perfect example of the union (that's growing as we speak, BTW) of Square and Nintendo.
~He could be a great 'WTF character,' much like Ness/Game and Watch were.
~It would probably push for more sales of SMRPG for the Virtual Console, as it will probably be out by that time (it's been confirmed for release, just waiting on it).
Now, all that being said, I don't think he'll be joining the party. Simply because I don't think Nintendo will want to go to Square and ask them for this, nor do I think that Square would offer it up. A lack of communication, my friends.
And now, even though I'm one of the biggest Geno-lovers the world has ever seen, I must give my verdict: 10%.
I have no nominees. I'm going to go cry.