Yeah, I see the streaming functionality as almost bigger announcement than the OS.

It's quite possible that one could stream into any other machine including tablets, laptops and even phones. This would enable playing your full Steam library from anywhere with decent enough connection (on both sides), especially games where input lag is not that big issue.

I really hope that this will be seamless. I would love to keep a beefy windows PC in the basement as a headless machine to run windows only games from and stream them to TV or Macs from there.