I'm hoping that the Wii U comes with a hard drive big enough to support multiple GCN titles (A typical GCN game is about 1.5 Gigabytes, I believe). I've heard speculation that it won't, and that a player will have to provide their own external hard drive to connect to the Wii U. With that said, it'd be fantastic if Nintendo implemented online features in some of the GCN games that were lacking them, or had them implemented, but poorly. Mario Kart: Double Dash!! comes to mind. There was a LAN option to connect GCNs for a larger multiplayer game, but it was quite a hassle to get two GCNs close enough to connect by LAN, if you even have a LAN cable and know how to use it, that is, AND for both GCNs to have a copy of the game. I'm not saying Nintendo should implement an online feature into every GCN game they release on VC, but multiplayer-central games like Mario Kart and Super Smash Brothers Melee could definitely benefit from it. Of course, there may be legal complications I'm not aware of to changing a game for re-release, as well as the staff that may be needed to maintain an online network for games, as well as to redesign the game for better online support.
Even with all of that considered, I have to wonder just how many GCN games Nintendo will even put on VC. There are only 21(?) Nintendo 64 games on the Virtual console right now. Some of the best N64 games will likely never be uploaded because of legal issues *cough* Rare *cough*.
With all of that said...
Melee and Super Mario Sunshine will likely be among the first to be uploaded. My biggest hope is that legal issues don't prevent Metal Gear Solid: Twin Snakes from becoming digitally available.