Sorry, but I don't like that idea. Many people would refuse to pay a Wii game they already own. Well that's what I think. I dunno.
I'm not saying anyone would like it, but it is what Nintendo has done in the past.
During the Wii's life we had a handful of titles from the Gamecube which were made to be played with motion controls, the new play control! series, with games such as Mario Power Tennis.
But your right many people wouldn't want to pay for games they already own, but hey I don't own Xenoblades yet so I really wouldn't mind that being rereleased on the Wii U Eshop for instance. But if they were released as Eshop titles and didn't hamper the development of new games, who'd be complaining?
This is what I want and I really hope Nintendo starts doing it soon (as long as it doesn't interfere with the production of new titles). Who wouldn't want Metroid Prime HD Trilogy, Twilight Princess/Skyward Sword HD double pack, Mario Galaxy 1 and 2 HD double pack etc.? Or even just sold separately as eShop titles? The Wii had some of the best Nintendo games ever made and there are definitely some I would rebuy so I could play them in HD and on the gamepad.