It's absolutely wild to me that they didn't include, and have devs ship profiles for some of their games, SuperDepth3D or some other depth map shader officially in some form in the Steam UI for this. If a big focus is playing your pancake library on a huge screen (due to there not being not many native VR games), having that huge screen be 3D would be a huge value add. And they're big enough to get some developers to ship profiles for their games officially guaranteeing some form of workingness(?).
This. This is what I am looking for. I remember using iz3d years ago, with their anaglyph renderer. Playing Half Life 2, Halo and others in stereoscopic 3D was a great experience. Dead Space was particularly nice, as the game uses no HUD.
I guess most of it could run as a Vulkan layer?
You can already do a lot of it with ReShade shaders like the aforementioned SuperDepth3D, but it requires a game profile, tons of fiddling and non-incompatibility from the game. Having that shipped as dev-tested profiles with games would be the exact sort of thing that makes proton nice to use on the steam deck