[officemonkey]

Steam lets me add non-Steam games to their launcher right now on Windows. Imagine the ribbing they would get from the hypocrisy of making a walled garden on Linux.

The bigger limiting factor would be "games that run on Linux." Does League of Legends play on Linux?

[StavrosK]

Well, that's just a launcher thing. Given that the OS will be open, I am pretty sure you'll be able to install it. The question is, will it be available on Steam the platform? I can't see why Valve would block it.