So the steam machine has finally arrived for those of you who don't wont a console or a great old pc sitting under your tv, get your gork on chaps!
On further inspection, it would seem that SteamOS is a Linux distro, so I suppose it stands a good chance of being quite capable.
SteamOS is just like Steam Linux in big picture mode with nothing else. I'm running Linux Mint at the minute (Thanks Obama/Windows10) with Steam on it and I've got 62 games playable out of 145 total games. Which isn't that bad considering it would have been 0 not too long ago. A lot of new games will be compatible in the future thanks to Khronos groups Vulkan api which looks to be getting a lot of support from developers. If you buy a Steam Box there is nothing stopping you putting Windows on it. There is also nothing stopping you building your on PC and putting Windows or SteamOS on it, or Linux for that matter.
Have you considered the fact that you'd be able to run more than half of your games if you used Windows?
TBH I've got kids so don't get to game much as is. The reason I'm on Linux is because Windows 10 fell over itself updating and after trying to reinstall 10 and Windows 7 with no luck. Well some luck but still with issues. I settled on Linux until I've got a bit more free time and the new image comes out. Thing is i'm actually really starting to enjoy Linux. Unlocking Android phones just got a whole lot simpler. I might see if I can get at my windows steam library through WINE.