If you look at the obstacles that prevent Geno from coming in you can see that his chances are very, very slim.
I mean, look at it this way: There are a fraction of secondary characters in Brawl, heck, I'll say 1/3. There's an even smaller amount of secondary characters that are retro In fact, there are none, but hey, it's not too straining on the imagination, so I'll say that it's a 1/6 chance for a character to be both a retro and a secondary character. Then there's the chance that there's a retro character that's a secondary character that's only been in one game. Now that's pretty slim, but it could happen, I suppose, so let's devide our fraction into a third, meaning now we have 1/18. Then the chance that that secondary, retro character that was only in one game is third party, and seeing as there will only be (most likely) three (at most) third party characters out of a rough estimate of a fourty character roster. Let's see, that's 3/40 of 1/18, so that's 0.00416... and then we factor in populairity, so that's taking off a third of that so now it's 0.0027... but seeing as it's on the poll, I'll ignore that. So now, we have Geno, who apparently has a 0.4 % chance. Mind you, this is a rough estimate, as this may be over or under a more accurate number.
So, Geno mathematically, would have an 0.4% chance, and everyone thinks that this is high? The facts do not lie, and all these numbers are smply based on facts drawn from simple common knowledge, and I sincerely hope that you people take my words to serious heart.