Pretty cool work, kudos!
This was exactly the premise behind the multiplayer SDK I made[1] but I moved to a middle ground (after feedback from devs) so to support existing languages and game engines single player game devs are familiar with but still easier than many other options out there.
We have now scaled it to many millions of players and it has proved worthy!
Wow, playroom looks awesome! It is great that it lets people integrate with all the existing libraries like ThreeJS for example. Glad to hear it has found its audience!