Feature Request: Screen Shaders

[esperanza-esperanza]

There does exist somebody else's project Reshadeck decky plugin, but it doesn't let us configure the shaders much, it does properly utilize the ability to change a shader at gamescope runtime doe(I assume it's some gamescope functionality).
Could we get official valve's sanctioned post-processing shader option?
I feel it could be popular for anyone playing older games and not just the old ones.
It would also require the ability to chain multiple post-processing shaders together, because some users want that.