I saw this interview with Vicarious Visions CEO Karthik Bal from Gamedaily that kind of confirms how we will be able to save our Guitar Hero 4 downloads.

GD:The Wii version of GH III plays wonderfully but owners have complained that the game didn’t offer any of the added downloadable perks that the Xbox 360 and PS3 games feature. We’ve heard that World Tour will have downloadable tracks?

KB: That’s right! Guitar Hero World Tour will be the first Wii game to offer downloadable songs through an in-game music store. Players can preview, purchase and download songs using Wii Points and we’ll have new songs available on a regular basis.

GD: With those downloadable packs, will players download that directly to the Wii’s internal memory or have you worked out a way to store those music packs elsewhere?

KB: Players can either download songs to the Wii System Memory or store songs on a SD Card, called the “Rock Archive”. When you want to play songs from the Rock Archive, players can create a custom set list, and then choose a venue and play!

So if this is true, it gives us unlimited storage, since once a SD card is filled, you just get a new one.

Full Interview from gamedaily