Well I'm not too sure how much longer the DS is going to sell for. It's been said many times that the DS sells like hotcakes, and I just went out to eat this morning and saw that almost no one had ordered any hotcakes for their breakfast. I believe this is a bad omen for the DS, and I think it could really just stop selling at any moment now.
I agree with everyone else that the Wii will definitely level off a bit sooner since most households will only have one.