We are going to release a standalone RoonSpeakers package that runs as a service. On a mac, this would live in the menubar. It would be accessible regardless of whether the remote is running/connected, and would behave just like an MS200–discoverable and controllable from anywhere on the LAN. This package is meant to solve your exact use case.
Private zones will remain private–they’re meant to address a different set of needs, and we don’t want to create confusion by creating two mechanisms to accomplish this.