One thing you could try is to setup an Authentik service and “federate” with these two providers. This way you could have internal SSO for your team, and proxied SSO for external users. Would be a bit harder, considering the need to host your own SSO, but maybe faster than having the OIDC plugin patched, depending on your capacity.
That said, I see (Corporate Login Provider) settings everywhere in Discourse settings, so it would indeed be nice to be able to add our own. Maybe forking the OIDC plugin and changing the names?