My position (for clarity) is that I agree that we shouldn’t try to update this TOML file as a way to communicate sdist metadata. OTOH, until we have a proper mechanism that’s portable, it’ll be nice to allow tooling to depend on these static declarations made through this mechanism that we’re introducing here.
This also ties in nicely with @pf_moore’s proposal over at Sdists (again): Metadata standardisation incremental update because it’ll then allow the sdist metadata file itself to use the same model as this file around the dynamic key.