It is an interesting idea. Imagine how many lego pieces are stored away in boxes because the owners don't know what to do with them.
Another thought, It could also lead to a revitalization of old lego themes. if someone sends a space police set, for example. And the kids REALLY love it, it might prove to Lego that there is still potential there. Assuming TLG pays any attention to what happens to the bricks once they leaves their hands. It seems like to good a chance for play-testers for them to pass up.