It seems like it can be possible to use relays(or a relay) for multiplayer game worlds, due to the fact that you can open two different clients using the same keys and access the exact same info when they are targeting the same relay.
In such a case, different relays could host different virtual worlds, which can be accessed from a game client held within a nostr app.

Now if someone can tell me how to integrate the Godot engine to develop on nostr, it could be possible to build 3D virtual worlds, or very nice 2D worlds. 
Probably though, there is going to be a bandwidth limitation, which may limit these worlds to a set server tick rate for any actions to be pushed.