Personally, I’d love to see this feature.
Right now, I build Haskell using cabal because I found the IOHK Haskell.nix implementation broken when I reached for it for a project with pkg-config dependencies.
Similar deal with purs-nix when Purescript rewrote spago and broke purs-nix.
It would be nice to finally build these two languages in Nix again with that lovely determinism I’ve grown so comfortable with.