Well, the DS has an upcoming change to it in the form of a newly redesigned DS. Nintendo already stated that it is ready for production. They are simply waiting for the current DS Lite to slow down in sales. It will eliminate the GBA slot for even smaller gaming on the go.
As for the Wii, the innovation has not yet even started. Example: What about the speaker in the remote? Wouldn't it be cool if let's say you could play your favorite songs through it while playing or could have an in game radio (like GTA) play through it during gameplay. The system itself has only BEGUN to get tapped. It has a 4 GB Flash chip in it. That has not been disclosed by Nintendo or any developers yet. Who knows what 4 GB of memory is for. Perhaps updated system memory? Better game storage? Who knows. I think Nintendo has (out of the 3) the brightest future. We all know the 360 has live which can do HD movies, etc. PS3 has the PSN which is live but toned down and free. The Wii has the free setup plus the addition of Pay2Play which no one knows what that holds. Nintendo has THE brightest future with THE most to gain.