Today your usecase can be solved ad-hoc by additionally manually signing what you push to keybase git, shared with the people you want to have read access.
If you want an encrypted storage solution with integrated read only access capabilities, I recommend using Tahoe-LAFS. You can probably store a git repository in it just fine.
If you want an encrypted storage solution with integrated read only access capabilities, I recommend using Tahoe-LAFS. You can probably store a git repository in it just fine.