Good news, since version 3.1.6 Really Simple SSL supports WP-CLI for basic SSL management. The Really Simple SSL commands can be accessed with wp rsssl. The plugin currently supports two basic commands: one to activate SSL (activate_ssl) and one to deactivate SSL (deactivate_ssl).
We would like to extend the plugins WP-CLI functionality with your suggestions. Please us know what functionality you would like to have included in the Really Simple SSL WP-CLI commands!