Shared library. I am not sure why this isn't getting more attention.
You have Steam, I presume. You know how the library works, you buy games via Steam or enter the CD key, and they're in your library forever. No more CDs, just download and play. XB1 has the same feature. Only in addition to your personal library, you can share your library with up to 10 friends. Those 10 friends can download and play whatever games you have bought, and you can download and play theirs. The caveat on all of this is that only the owner and one friend can play the game at the same time, but still. Ignore the "PS4 sharing video", this kicks that right in the teeth. Not only do you not need to hand your friend the disc, but simply by virtue of owning a game, you can always have a friend hop in for multiplayer with you.