Support for other PGP implementations and remote keys

[zugzwang]

It is nice that git-crypt reads the gpg executable from the git config gpg.program configuration. This allows one to interface with other PGP implementations, as soon as the desired commands can be rewritten in terms of gpg CLI. For instance, we achieved this with a fork of Sequoia-PGP that allows to keep keys inside an HSM, instead of local keys.

It would be even nicer to either

• be able to interface directly with sq
• interface with any implementation of SOP (which includes at least 8 PGP implementations, including gpg - see this)

Apologies if this has been already discussed/considered.