Importers as independent packages?

[Martin Becze]

Hello Guix,
I have been working on a recursive importer that uses semantic
versioning over on #38408. It relies on guile-semver. I'm not exactly
sure how to add guile-semver as a dependency to guix. But I'm also not
sure that I should. Importers will probably not be used by the majority
of end users so would it make sense to put the importers in their own
package? This would also nicely solve recursive-import-semver's problem
of being dependent on guile-semver. 

Also in the future it would be nice if the crate import could read from
a Cargo.toml directly (this will make importing things like alacritty
much easier since it is not crates.io), which would probably mean have
yet another dependency (guile-toml). What do you think about this Guix?

Thanks,
-Martin Becze