Phoronix article: https://www.phoronix.com/news/Steam-Machines-Frame-2026
Also listed here: https://store.steampowered.com/sale/hardware
Valve has already sent support for the new Steam Controller upstream: https://www.phoronix.com/news/New-Steam-Controller-SDL
I forgot where but some time in the last 3 hours I read that the goal for steamOS is to be supported on all PCs, though it's an ongoing effort.
That's a big challenge, but a worthwhile one. The reason that Microsoft exploded in the DOS era was because it ran on everything that was "IBM compatible" aka x86. Meanwhile Apple was over there with a competitive product, but you could only run the software on their OS that ran in their hardware. People were able to get cheap third party x86 compatible computers and run MS-DOS (and later Windows), and they were not locked into a specific vendor doing top to bottom hardware/software support.
If they do this right, they'll be the go to option for a lot of people who generally use their PC primarily for gaming.
Not to mention that Steam does have competition as an app store, stuff like GOG. I mean, it's a little bit obnoxious to use both at once, but really not that much of a hassle.