A part of an MTV (fan written) interview with Harmonix…
MTV: ”About the Wii Points, does that mean I have to have Wii Points already redeemed on my console before purchasing new tracks? As for the SD card streaming, does the game read those tracks 100% from the card? If so, could this mean Nintendo is open to letting full-blown games run 100% from the card?”
Harmonix: You have to purchase Wii points before booting up “Rock Band 2,” yes. But once the songs are purchased, “Rock Band 2″’s in-game store can take advantage of those points. You don’t need to purchase new songs from Nintendo’s storefront channel.
“Rock Band 2″ does read 100% from the SD card, but it doesn’t appear Nintendo will be allowing for games to be executed off the card just yet.