There was a bit of talk earlier about releasing HD versions of Gamecube games via download, and it's something I've been thinking about for a while, so I figure I may as well post my thoughts on the matter.
First, though, a bit about the Virtual Console on Wii U in general.
Virtual Console
There's no technical reason why the entire Wii VC collection shouldn't be available day one on the Wii U. The console is backwards compatible with Wii software, and all the VC games are Wii software. Hopefully they'll have the full lot on day 1 (it'd be a good selling point), and then upgrade them with save states/etc. later on, as they're doing with the 3DS ambassador games. I am a little worried that they'll redo the emulation from scratch, though, and we'll end up waiting years for everything again. Either way, I'd imagine transferring purchases from the Wii is pretty much certain, given that they did it from DSi to 3DS.
Furthermore, there's pretty much nothing stopping Gamecube games appearing on the Virtual Console right from the start. The Wii backwards compatibility again means Gamecube games will be almost trivially easy to get running on the console. They're undoubtedly going to phase the releases out over a few years, but there's no reason not to see a couple of Gamecube games appearing on the Virtual Console every week. I'd say it's extremely likely we'll see Wii games on the Virtual Console too, but not until physical sales dry up, a year or two after launch perhaps.
A wonderful (although very unlikely) VC feature would be to share GB/GBC/GBA/NES/SNES/etc. VC purchases across both the 3DS and Wii U, and to feature cloud saves to sync progress between them. Hell, you could even include DS games in that list, although I shudder to think what some of the 3D ones would look like when blown up to 50".
In general, the VC shop on Wii U (and the Wii U eShop in general) needs to be much better laid out, a lot faster to navigate, and with full-screen screenshots and videos for all games. The 3DS eShop is a big improvement in this regard (although still not fast enough for my likings), and hopefully they can make the most of the HD screen and touchscreen. Also, they really need to start doing sales on the eShop. Steam-style daily deals would be a great way to promote lesser-known titles.
Virtual Console Plus (or HD Classics)
While regular VC games are effectively ROM-dumps, my thought for HD versions would be to treat them as ports, with (obviously) 1080p/60fps support with widescreen/AA/AF/etc., but also with added features taking advantage of the Wii U pad and other Wii U features (the obvious example would be Zelda games with the inventory and soforth on the touchscreen). While the name HD Classics would fit with the 3DS's 3D Classics, I feel that the name Virtual Console Plus would better emphasize that it's more than just HD visuals that have been added.
The ports shouldn't take too long, perhaps a couple of months each with a small team (preferably including at least one or two of the original developers). CPU code for Gamecube and Wii should run without too much trouble on the Wii U, so it would mainly be a matter of porting TEV code over to the Wii U's GPU architecture. Given that ATi/AMD designed both, they should be able to provide guidelines for the porting process. Redoing menus/UI elements in HD and getting stuff running on the touchscreen shouldn't be too labour intensive either.
To get an idea of what I'm thinking of, here are a few potential VC+ games that I think would work pretty well:
Zelda: The Wind Waker
The obvious one. The game looks great on Dolphin, but it'd be so much nicer to have an official, glitch-free HD version of the game to play on a big-screen TV.
Extra features: Inventory, maps and so-forth on the touchscreen. Also, touchscreen Tingle Tuner!
Mario Galaxy/Mario Galaxy 2
Would look glorious in HD. Due to the limited (but necessary) use of the pointer in each game they'd be limited to Wiimote control, hence no touchscreen stuff, though.
Extra features: Not really sure. Perhaps some co-op mode where the second player uses the Wii U pad somehow?
Metroid Prime/MP2/MP3
Sweet, sweet Metroid. You know Retro would be happy to handle these, as they volunteered to do MP Trilogy on the Wii.
Extra features: Choice of Wiimote/Upad controls. Use of touchscreen as map, or as an augmented reality visor. Would be sweet if Retro could add fancy modern lighting effects to really heighten the atmosphere as well.
F-Zero GX
If you don't want to play this in HD you really need your head examined.
Extra features: A long shot, but online multiplayer would be wonderful, as would (and this is an even longer shot) a track editor on the touchscreen. Also, while I don't expect Nintendo to go for 3D in any of their own games, this is one I'd like them to make an exception for.
Star Wars: Rogue Leader/Rebel Strike
It's sad that Factor 5 aren't around any more to make a sequel to these, but perhaps Nintendo could hire a few of them on a contract basis to make VC+ versions of two of the most technically impressive games of the SD era.
Extra features: Four-player co-op, competitive multiplayer. Use of the touchscreen as a radar and AR targeting computer.
Killer 7
To my eternal shame I've never actually played this, but I can imagine it would look great in HD.
Extra features: Damn if I know.
Resident Evil 4
I know there are already HD versions for PS360, but it would be great to have a version with options for both Wiimote controls and classic controls.
Extra features: Inventory on touchscreen.
and soforth.
There are probably two inevitable questions at this stage. Firstly, where are the N64 games? While I'd love to see some N64 games on VC+ (sweet jesus F-Zero X with the 64DD track editor would be glorious), they're generally not going to hold up as well in HD and they'd be a lot more difficult to port, due to the N64's crazy architecture. It'd basically be a whole lot of effort for very little gain, especially when you consider that VC versions of N64 games can run at higher resolutions anyway.
The second question is likely to be: Why go the downloadable route, why not retail releases? Basically, while HD Mario and Zelda retail collections would sell like gangbusters, I can't really see the same thing being true for many other games. Even if the cost of making a HD version of, say, Killer 7 might be pretty low, the costs of printing, distribution etc. would make a retail release infeasible considering it's a niche game. With DD, though, a wide audience can be reached at very little cost, and pretty much every penny from sales goes straight to Nintendo/the publishers, allowing the port to break even much more quickly.
To get a retail presence for the more popular VC+ games, Nintendo could sell game-specific download cards at shops. The NFC cards would come in a mini version of the Wii U game case, and all people would have to do would be to wave the card in front of the controller and the game would start downloading. It would both keep retailers happy and at the same time provide a way to transition customers to digital distribution.
In fact, to encourage people to buy a Wii U brand hard-drive to store all these games, they could include a popular VC+ title pre-loaded onto the hard-drive as an incentive. I know if they included, say, Wind Waker+ on a Wii U hard-drive and said you wouldn't be able to get it any other way for at least 6 months, I'd definitely pony up the (most likely quite high) mark-up over other hard-drives.
With decent planning, I'm sure Nintendo could get one VC+ game out each month, and that would give them quite a few years of releases, and higher profile ones could perhaps help fill some gaps in their retail release schedule.