and?

potato

The point of SteamOS is a pre emtive attempt to distance reliance on a microsoft platform. Mainly to keep control over what steam decision makers consider "theirs". Making the OS a sort of, open project....free? Is to give it traction. Similar to Android.

Shut out gog? What would be shutting out?

Developers will maintain the status quo. Sticking with an ever increasing dumpster fire after another, that is microsoft.

What would this change about the status quo?

Steam already controls the majority of the market on Windows. It would just mean one less annoying middle man for them since they could kick out a lot of unwanted legacy junk if enough people migrated from Windows.

It is unlikely that enough gamers will abandon Windows for Steam OS. However, it is supposed to run on the living room / home theatre computers that are already running a specialized Linux distro. As such, the threat is less towards MS and more towards Linux, it looks like "embrace & extend", though ATM the extensions seem more like a custom Desktop Manager, which wouldn't be inherently evil, except for being closed source, and could probably also be run on other Linux distros.

Linux not having galaxy version is actually a plus! Not even Temple OS?!

It's literally just Arch, KDE 6, and a fancied up Steam view. Proton is just a fancy Wine and contributes code back.

In that case, it would be a slight plus even. Having a big player actually contributing code often is a win-win. Plus, I just stumbled accross Steams own announcement where they explicitly state that people can install their own launchers and games.
But it seems like they could block access to other launchers or executables, say by signing or encrypting their own Steam executables, as their DRM does for some games already, and refusing to launch anything unsigned, but then people would likely just go back to vanilla wine and spread the word, which would be bad for everyone.

@FarkyTheDog: If you're referring to the sad state that Galaxy development seems to be in, then adding another version to maintain would certainly not be helping, agreed. However, I wonder if the lacking MP facility in some games isn't directly related to Galaxy missing, because frankly, Linux has always been very good at two things: file systems and networking, so there's no technical reason why it wouldn't work on Linux while it does on Windows and even Mac.

That and it being a plus to skip achievements and other unnecessary bloat of galaxy.