I did not find anything related to Steam licenses in the whitepaper. But on TechCrunch I found:

“Users can use their own Steam library with our service, buy the game from Steam directly, or purchase the key and subscription from us.”

I think they will be setting up virtual machines for each user, otherwise the Steam libraries and save games from different people will conflict with each other. The downside is that if the game data is also stored in the virtual disk of the virtual machine that will waste a lot of storage space on duplicate bits. But that too can be solved by configuring the virtual machines with a shared virtual disk for game data and separate virtual disks for user data.