Nintendo and Sega have already struck a deal to offer Master System and Mega Drive games on the Virtual Console if I'm not mistaken. I think 32x, Saturn and Dreamcast might not be possible due to the Wii's lack of hard disk and general underpowered nature. Even if it does happen, the chances of third-party games (e.g. Rayman) showing up on it are slim, as there haven't been many third-party games on any Virtual Console system so far.
According to some leaked documents for Sega, Dreamcast games will be released on PSN. Mentions of exclusivity deals imply other platforms as well (XBLA, Steam etc.). I don't care too much about this though. I'd greatly prefer to have unofficial emulation of these systems progress, as it can offer a far superior experience to playing the games under any official service.