So far most rumors for rockband Wii are pushing for a late summer release like July-August
RB:2 is rumored to come out for christmas sales again this year, so it could work out.
The people that really want RB:1 on the Wii will snatch it up play it for a few months then get a new game. For everyone else im sure they will offer a big combo pack of RB:2 for the Wii aswell. Unless they push off RB:2 release for the Wii wich would be a bad call considering all the casual gamers that own Wii. They love thier peripherals, without a Wii version aswell they will loose out on a good chunk of market share.