The Nintendo Wii system update 4.0, will allow downloaded WiiWare and Virtual Console games to be read off an SD card, plus Nintendo are now allowing this feature to be used by full retail games. Guitar Hero 5 will be the first retail game to take advantage of being able to stream in-game date from an SD memory card.This enables players of Guitar Hero 5 to be able to download content and store them on an SD card and play the songs from that SD memory card. It also avoiding having to shuffle the data from SD card to the Nintendo Wii's internal memory every time you want to play a different song, but don't have enough room in the Nintendo Wii's internal storage to keep all your downloaded songs.
Guitar Hero 5 will be the Nintendo Wii's first Guitar Hero game to accommodate all types of DLC for it. The previous versions of Guitar Hero on Nintendo Wii required every separate song to be downloaded on it's own, with Guitar Hero 5 being able to read from SD cards, users can now download the full album.
There isn't any news on what other games and publications will take advantage of this feature, but it is hoped that it will be used well by other companies and Nintendo Wii users can enjoy even more DLC.
Source: MyWii.com