It will be interesting to see if any kind of marketplace for trading games is in the works. Selling games back to Microsoft would be worst-case scenario, I think. You aren't selling any physical copies back to them, you are returning your license. There is no physical product that they would have to turn around and resell. It's like goldsinks in MMOs. By selling back to Microsoft, you are removing your copy of the game from the marketplace, and MS can sell another license at full price. You've effectively rented your game. If, however, you can trade games, things become much more interesting. How do people place value on certain games becomes a very interesting topic. Can MS offer a more compelling reason to sell them your license? Or would you be better served trading among the general public(assuming this is even an option)?
Gawd, all this talk about licenses and digital rights is really weird. It's like, in one fell swoop, MS has managed to bring the issue of digital ownership to the forefront of the tech debate. It really should have been there a long time ago.
Again, I wasn't planning on buying a One at launch anyway. This reveal did nothing to change my mind. At this point, it will take some truly killer "app"(in light of this reveal, that seems like such a poor choice of words) to get me on board. I expect a large amount of games worth buying will be multiplatform, for which I have my PC(and, yes, these DRM schemes already exist there without the option to sell).