I'd quite like to see the Master System on there. It's perfectly feasible, and it did fairly well (I believe it actually beat the NES in Europe) so I don't see any reason why it couldn't happen. Phantasy Star and Zillion would be cool to see on VC.
Also, the Saturn. At one time I thought they couldn't get the games on there, but after seeing Turbo-CD games added recently it would seem it is possible. Of course, the Saturn is a big step up from the Turbo-CD, but I think it's possible I'd like the chance to play Panzer Dragoon Saga and Shining Force III.