Gladly it’s in development and have been discussed and requested many times over the years Mobile Music Sync and Streaming [On Roadmap]
For a service that has a subtantial price you could just expect a core feature like this during this age and time. You are forgetting it’s not announced yet and painting a too black and white picture of the feature that it would be “always on” with full bandwidth without any cache/syncing/latency optimizations that would make it sensible to use. Like in Subsonic/Plex/Ampache/any similar services out there.
I’m also quite sure it wouldn’t be forced to be enabled for all users because I know many prefer to just have their home theater system and user roon like Sonar and equivalents for example. I like to think Roon Labs want to listen to their paying users, old and new.