It will be interesting to see what this does to the state of GL support, Wayland, scheduler, etc. Steam telemetry will give Valve a lot of data about how different hardware/software/driver configurations are working but on Linux they'll be able to actually push patches to distros if need be. I would love to see Valve profile Source on Linux and start shaving sources of latency and jitter, it could eventually be better than Windows for competitive gaming.
Hopefully this pushes them to support more variety in the underlying operating system as well. I still can't get Steam to run on my Mac because I made the apparently rare decision to format my machine as case sensitive filesystem.
Incase anyone's curious about the stats Valve currently has from the Steam Hardware survey on Windows and Mac OS X here's a link to their pretty cool stats page which looks like its recently had a bit of a facelift:
