So far, this isn't wowing me, but I'm interested to hear about the rest of Valve's plans.
Thus far, it doesn't seem like a good addition to the hardware I already have. That's a big TV with a console and a (non-gaming) HTPC hooked to it, as well as a gaming/Rift/office PC in another room. It seems silly to build another box to connect to my TV, one that does nothing but play phone-class games and stream PC games from the "real" gaming PC. And I can't run the Steam OS on my HTPC, because then all my Windows Media stuff goes away.
Well, I guess I could just install Steam OS onto the gaming box, and connect it to the TV. I suppose that might work as a console replacement, but only if the software support increases dramatically and quickly.
Like I said, I'll be watching with interest.