The rumor that Sega Saturn games will be appearing on the Wii Virtual Console has been making its way around the web for some time now, but it's picking up steam again due to some chatter coming from a DigiPen student. (The game design school is adjacent to Nintendo's headquarters.)
Nintendo certainly could go down that road if it wanted to, as evidenced by the large downloads available to those using Internet-enabled PS3s and Xbox 360s. And, as many pundits have already pointed out, Sega and the big N sure have been chummy as of late.
So, who knows? We know more systems (at least one) have yet to be announced for the VC, so the Saturn is as plausible as any.