Don't like the overpriced Steam Machine? Just build your own and put SteamOS in it
Seems a bit unreasonable to call it 'overpriced'; it's hard to get equally-specced parts any cheaper at the moment, and it's all wrapped up in a neat, small, integrated package.
Being able to run SteamOS elsewhere might help convert more people to Linux, but the obstacle identified here is NVidia driver support, as usual. Steam has been very easy to install on every Linux distro I've ever used if you're still wanting to use it as a general purpose machine, but having it all wrapped up would be nice too.