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
In their announcement video, they specifically called out that you can install whatever software you want and showed somebody working on CAD. So, yeah, definitely.
I think they mean SteamOS on other hardware, like a custom built PC.