Maybe taking a little page from the Xbox One, someone on NeoGaf has found some code in the latest Steam beta build that might hint at a future ability to let you borrow and lend games to friends. The code found in particular says:
SteamUI_JoinDialog_SharedLicense_Title" "Shared game library" "SteamUI_JoinDialog_SharedLicenseLocked_OwnerText" "Just so you know, your games are currently in use by %borrower%. Playing now will send %borrower% a notice that it's time to quit." "SteamUI_JoinDialog_SharedLicenseLocked_BorrowerText" "This shared game is currently unavailable. Please try again later or buy this game for your own library."
If that's the case, that's a pretty big change in the PC world where lending and borrowing hasn't been done in ages. I'm guessing this will be on a publisher by publisher basis, but it would be a really, really great feature for the PC side of things. There are plenty of games I have just sitting around in my Steam account that could be put to good use for some of my friends to try out. I'd also love to try out some of my friend's games to see if I want to pick them up myself.
Xbox One might have been touting their share feature, but Steam might be ready on their end as well with another feature for PC gamers that console owners once thought were just available to them.