Has Alan Rickman done much voice acting? Only thing I can think of was the Marvin the robot in Hitchhiker's Guide to the Galaxy.
Btw, for those of you who are not familiar with Alan Rickman, he was most notably Snape from the Harry Potter series (blech... harry potter...), the Sheriff of Notingham in Robin Hood: Prince of Theives, and Dr. Lazarus from Galaxy Quest. At least, that's what I know him from, the guy's done a good bit of acting.
Anyhow, as pesimistic as I am about more Mario characters, this one might be a good fit. That is, he's far less generic than most Mario characters, and has a personality to boot. He's not a part of the mainstream Mario games, but he's also not from the spinoffs where characters are just different models with slightly altered mechanics (i.e. Mario Kart, Mario Party, ect.). In essence, he seems as though he could function as a character independent of any association with Mario, which is something that almost none of the supporting Mario characters which are not already in the Smash Bros series are (e.i. Waluigi has no significance unless he's associated with Luigi or Wario, Daisy has no significance unless she's associated with Peach or Luigi, these characters are completely defined by their relationships to other existing characters).
All of that longwinded explination to say that I agree with the lot of you and would be pleasantly surprised with the presence of Geno in SSBB.
Andy