I find it difficult to believe, or at least to understand, why in god's name it would take a year. A dedicated team could put it together from scratch in a year. They already have the vast majority of resources in place. The PS2 version is already out. That's 95% of the artwork, the songs, etc. etc. And, surely they've already been working on it before now. I can't imagine the brisk sales of the Wii could have gone unnoticed by EA over the last year.
Let me be the first to say, though, thank you god in heaven for this. Rock Band and GTA IV are the two games that I was planning to be ultra depressed about not being able to play over the next year or two. Restraints on my free time and finances make getting a PS3 before then virtually impossible. But if Rock Band is out for the Wii by August or December I can hope for it as a birthday or Christmas present. We shall see.
BTW,it will have downloadable content. If Guitar Hero III hadn't already been released for the Wii, maybe up to a year earlier than Rock Band, EA might be able to get away with leaving that feature out. But if Guitar Hero can do DLC on the Wii, there's no reason Rock Band can't. Color me excited.