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


Maybe. As it stands Valve is rather open with their implementation, but who’s to say it will remain indefinitely so.
I do get the desire, though. I’ve gone to Bazzite and Fedora and – even though it’s a lot better than just a year ago – it still requires some commandline tweaking. It isn’t entirely smooth sailing yet.
Will SteamOS be? I do have some doubts.
FWIW been using SteamOS on the SteamDeck for ~3 years now and from gaming to tinkering, no major problems. Never had to tinker hard or re-install. A couple of time it didn’t suspend properly or I had to hold power button of to force a shutdown but that’s about it.
I doubt Valve would back of from the openness because that’s their one single advantage.
Not on the short term, but who knows. If SteamOS becomes a major player in the PC space, at a post-GabeN Valve–
But that will take many more years, if ever it does happen. I do think it is a legitimate reason to be somewhat cautious.