After seeing the new-ish cargo metadata lints, I was thinking it would interesting to have a lint like:

crate_license
Check the license information in the crate metadata and restrict to something.

I imagine a whitelist/blacklist of licenses would be what most want.

# in clippy.toml
blacklisted-licenses = ["MIT"]
whitelisted-licenses = ["MPL"]

This seems fairly straightforward to implement after reading some of the source for the cargo lints. If we want to do this I'd love to try to implement.