Linux gaming has improved every year. The only area it's losing support from is from Valve. Really, when was the last time Valve released a successful new product?
As for Steam machines, the release was it's doom. Who the hell wants 50 different machines to choose from on a platform that hasn't proven it has a large enough game selection to warrant any significant money should be spent on it?
The idea was insane. There should have been ONE steam machine. It should have been from Valve, or with some partnership with Alienware or whoever they wanted.
It still would have failed, but it would have had a better shot.
I am convinced, the last place Linux will grab a significant market share from is from the desktop (with gaming tagging along for the ride). Meaning, it's already everywhere. It's on your phone, in your tv, your router, your car, any electronic device with internet access. It powers your search engine, the stock market, almost everywhere you go on the web.
It's free and as long as companies can leverage that it's going to creep further and further in to everyone's life.
Microsoft is reorganizing (again), the Windows division is losing importance. It's obvious to everyone, even Microsoft, that it's not going to be a big part of their future. It's a dying product. Microsoft is going to make money from cloud based subscription services, game making, entertainment options, etc.
You already own 50 steam machines.