Okay, but... how? You can't serialize a function or a closure very easily. I'm unaware of any language which attempts to do so.

Not having functions as values (true of pretty much any serialization scheme I've ever seen) makes serialized data structures strictly less powerful than data structures in code.

> that needs to be used by another frontend

I don't think this was ever a goal of Nix. But if it was, well, you would end up with something considerably less powerful for the reasons I stated.