I'd prefer that. I mean, the XBox One and PS4 will have custom AMD Jaguars, but if the last generation is any indication, they'll still be around in 2021. There have been several generations of PCs since 2005. My PC is "old" by PC standards but it's half the age of the 360. Heh, that puts things in perspective; I have a GPU that was low-end when it was new and it's a few years old, I have an AMD X4 630 CPU, and I was marveling at how smooth all the Linux-native Steam games I have so far seem to run. I'm guessing my PC will be obsolete once all the new consoles come out, though.
Off the shelf hardware means, in theory, that you're not constrained to older hardware.
I'm not sure how I feel about big picture mode. I have an HTPC running Gentoo (yeah, I know) and running it on my TV is...meh.
There have been rumors that they've been working with Xi3 but that would likely mean they have something new in the works, as none of their current line would make for a modern gaming experience. It would be kind of neat if Valve put out a gaming PC that could go in a VESA mount, though.