This is so aswome! straight from Mehdi:
It's a "family" affair
Since its announcement, there has been some confusion over the details of sharing your Xbox One game library with up to ten "family members." Mehdi couldn't give comprehensive details but he did clarify some things.
For one, a family member doesn't have to be a "blood relative," he said, eliminating the extremely unlikely possibility that the Xbox One would include a built-in blood testing kit. For another, they don't have to live in the primary owner's houseI could name a friend that lives 3,000 miles away as one of my "family members" Mehdi said.
You'll be able to link other Xbox Live accounts as having shared access to your library when you first set up a system, and will also be able to add them later on (though specific details of how you manage these relationships is still not being discussed). The only limitation, it seems, is that only one person can be playing the shared copy of a single game at any given time. All in all, this does sound like a pretty convenient feature that's more workable than simply passing discs around amongst friends who are actually in your area.