and what are you going to do when you want to run Steam Directx based games? it says it will have a "stream" function = you will need windows for that.
or what about playing a EA game? they will never be obviously on steam so what you gonna do? or a mmorpg, you know... most mmorpg are windows only. with exceptions like WoW but of course you wont see WoW in a Linux, because you haven't seen any blizzard game ever in a OS other than Windows and OSX.
do you think people will give up their games? their cracked games? their emulators? last time I saw a video of a boy running MediaPortal (a windows only app) and it has a steam plugin, and yeah, plugged on a tv and you could access it easily in a HTPC software. he used a xbox controller for that... it ran good with no problems.
just look at the steam statistics... every OS go down but windows 8 and 8.1, so even Linux being free, their steam usage goes down? you can check it yourself. so its like... I don't see how this steam will be popular when you can always get a console with a huge game library like 360 or ps3, with a lot of games that will never come to PC.
and I don't know why people would want to change their windows OS, that they can plug it in a tv and have more games that they would actually have in a steam OS. because again, its not like every mmo, or EA games, or blizzard games will be on steam OS... and a lot more games.
so while I know people like Steam so much and hate Microsoft, well...the % of the people that would get interested in this OS would be minimal. its silly to think "oh steam OS, I will ditch Windows now" and then think Windows will be dead or this will be a threat for windows. when not even OSX with more marketshare could do anything to windows having nice games like diablo and WoW and stuff.
the majority of people I don't think will change their windows for steam even if they seem to love steam so much. its not like steam is the only way to get games in a pc, that's the thing. not everyone play steam only games. and I think that's the big plus for Windows.