The Virtual Boy would be impossible to emulate on the DS, it used special screens to create the 3D effects.
Plus I highly doubt Nintendo wants to being attention to their biggest failure.
It wouldn't be impossible. It just wouldn't be in 3D, that's all. I believe there are VB emulators that exist on the PC, so it theoretically could be done on the DS as well.
But of course, your point about Nintendo not wanting to draw attention to their failure is probably valid. Then again, the VB is rather old now, and few people remember it or have ever even heard of it, so it wouldn't be too embarassing to draw attention to it now, I think.
Again, I think the games would just appear as regular 2D but should still be fully playable. So its something that COULD be done.
Edit: Then again, what if Nintendo surprises everyone by making the DS2 be a 3D system? The VB was a flop, but the technology wasn't mature in those days. If Nintendo attempted it now with current technology it would blow everyone's minds and it would really put them apart from Sony and its (presumably) 2D handheld. If you look at what Nintendo has done this gen with touchscreens and motion controls, I don't think them pulling something like that is out of the question.