this is pretty cool! what I do for my project (3d voxel web page platform) is treat the scene as a document and push updates to the server when things change. this works well for distribution and simplicity, but does mean multi-player is "difficult". using spacetime to manage and track that info and have threejs render would be cool and enable a lot of things.

I may explore spacetimedb as a project sometime, although i am reluctant to be tied into a platform that my project cannot work without, that i cannot host myself, that can change their pricing/limits/terms of at any time and for which there is no alternative.