This looks very promising. There's a need for persisting game state in a central place, but also have that data streaming in.
I'm wondering about temporary gamestate that doesn't need to persist. Things like terrain or destructible voxels, where the size could be prohibitive to keep in a databases, but would work well in memory or with a cache.
Great question about the non-persistent game state — Implementing a custom setup on your own server is likely the best approach paired with CDN if alot of people are downloading.