Does/Should Hydra upgrade derivations to fixed output

Should derivations if they are reproducible choose to opt-in to be a fixed output derivation ?
(i.e. intensional)

I don’t really pay attention much to the derivations I’m writing whether they are reproducible
however it would be interesting if hydra or a separate system that is running build-repeat on NixPkgs to find those that can be upgraded to be fixed-output?