This would be great to have in SOPS. Makes the secret story much better to be able to encrypt for a recipient, without having access to their KMS.
This is a pattern we follow, so can't adopt SOPS yet, to encrypt offline without touching the environment. It also allows developers, who do not have privileged access to production environments to pass us secrets for target systems.
https://github.com/getsops/sops/issues/684