I am under the (potentially mistaken) impression that at minimum rasterization and texture filtering retain dedicated hardware on modern cards. There's also the issue of the format you output versus the format the display hardware works in natively.
That said, I'm not clear the extent to which such dedicated functionality either already is or could be made accessible via the instruction set. But even then I'm not sure how ergonomic it would be to make use of from a shader language.
Are there any fixed functions left that aren't just being implemented by the general compute shader hardware?
I guess the ray tracing stuff would qualify, but that isn't what people are complaining about here.