I suppose you mean using NixOS on a steam deck, right?
And if so, yes, but not exclusively.
This is currently used successfully on different systems.
What Jovian NixOS does is actually integrate the Steam OS experience with NixOS. Not just superficially so by… whatever the heck this is supposed to do:
{
programs.bash.loginShellInit = "steam-gamescope > /dev/null 2>&1";
}
This will not support switch to desktop, and is absolutely not a proper way to handle anything remotely close to ressembling a graphical session. This will be missing a lot of what session handling actually has to handle.
This will also be missing a few of the services expected by the Steam OS experience from steam, so things like the power button working as expected will not be working as expected.
You’re stating “Looks too complicated”, but then, you have stuff that is uh… Stuff that is looking like it is simpler, but in the end are having complicated consequences when considering how a Linux distribution operates.
Some observations follow, just from looking quickly.
This makes it impossible to just include the config, you end-up having to vendor it.
Everyone’s on the US west coast, right?
Why the long string with as\s*steamos
?
BTRFS(?) expectations without making it mandatory, or even documenting it:
This looks too complicated. That’s a heavy-handed approach at “defaults”.
Also, somewhat scary defaults, considering autologin is setup:
Other scary default 
This shouldn’t be in a configuration you could import:
Vendoring-in some “Steam Shortcut Manager” like you did is somewhat questionable, though not necessarily a problem. It just seems odd that it also includes a shortcut.vdf
in the repo, with some of your personal (test?) data. And having the __pycache__
folder being included, is odd too.
Comparatively, what Jovian NixOS does is try to follow the normal NixOS semantics, so that there are no surprises from including the configuration in your system configurations, even if you don’t intend to activate it.
Activating features is done via a tiered set of options, which allows either going for the trivial “everything”, or opting-in into more discrete features… or even opting-out, via the same tiered options.
While this visibly adds complexity, this ensures you’re not forced into every choices the authors are making.
Additionally, making the switch to desktop option work as expected is considered a basic feature. It is, imo, a major feature of Steam OS, and shouldn’t be ignored.
And we’re doing it in a way that works better than on SteamOS: you can pick your desktop, and your username. After all, it is for your computer, even if it behaves like a video game console.
It generally should slot into the configuration you’d be using on your other systems, with the main caveat that the display manager has to be configured differently. Otherwise everything else follows the semantics from NixOS.
As an additional note, there is no “integration” for updating non-steam content within Jovian NixOS. It’s because this is a really hard problem, as it involves diving into the internals of Steam, without any method to tell Steam to update its view of the files, and additionally, without having a proper “lifecycle” where we can include the data even without the user having been logged into steam at least once.
But if you want to imperatively edit your non-steam content, there’s also this that I made: