Comment by ac29
> Sure this could probably be a package in a more "traditional distro", but I'm almost sure most people don't expect their Display Manager to be replaced with Steam when they install a package.
You can add steam big picture mode as a session type which would let you pick it from the login manager (the same as if you had both GNOME & KDE installed, for example). There would be no need to replace anything.
Doesn't work as seamless, NixOS has this option but you can't quit the session unless you go to TTY and type `steam --kill` (the button for `Switch to desktop` exists but doesn't work). For it to work AFAIK you need to give SteamOS kind like a Display Manager permission (and also have some shims that does the actual work for switching sessions).