Let's be honest, SteamOS is done. Steam got exactly what they wanted from Microsoft and dropped it like a hot potato (so sorry, you'll never get to use that cool controller).
Consider that for decades Microsoft has not allowed anyone, anyone to touch the user experience. Even after Netscape's antitrust lawsuit over active desktop, even after BeOS withered and died hoping someone would sell a windows computer with dualboot, or hell just a windows computer with a "Setup BeOS" icon on the desktop. Steam is facing the Microsoft Store and a real threat that the Microsoft Store will become the way to buy programs (see also: iOS). Steam trots out SteamOS, and Microsoft snickers. The hype train builds up, and Microsoft sweats. Games start to port and Microsoft snaps.
Alienware ships a Windows 8 PC that boots to Steam instead of Metro.
Now, let's step back a second and look at the big picture here. At the time, windows 8 adoption is absolute total shit, swirling the drain of a public restroom that hasn't been washed for years. The last windows evangelists are all hanging on imploring people to just try it out, just give it a chance, and oh by the way install Start8 to fix metro. Think about that. PC vendors are on the verge of revolt, their customers refuse to buy their goods, and all for the want of installing a $5 program to fix the metro experience. Best Buy is probably screaming at Microsoft, begging them to allow them to remove the metro experience so they can move their inventory. Hell, they're probably begging them to let them advertise their Geek Squad services to "optimize" the experience and install that $5 program for $100. But no, the Microsoft Experience is inviolate, the holiest of holies, eternally immutable. No matter how much hatred it gets, it Must. Not. Be. Changed .
And then Alienware ships a Windows 8 PC that boots to Steam instead of Metro.
SteamOS's job is done. When no-one was looking, Steam took Microsoft and snapped it like a twig. We'll never know exactly what dark magicks were invoked here, but in the blink of an eye, Valve routed Microsoft in a war that nobody even realized was being fought. When Japan makes an anime out of this event, GabeN will point at Steve Ballmer, say omae wo shindeiru and Ballmer's head will implode, without GabeN throwing a single visible punch.
Steam OS will probably putter along, we'll probably see a few things be trotted out to keep the dream alive, after all the hype train did build up a lot of steam (pun not intended). Eventually a few of these AAA developers will say "it's really just not ready for the prime time" and we'll go back to getting a few wine ports and indie games from hardcore dedicated guys who just really love Linux.
But the masses will probably never get to hold that controller.