I'm interested in the concept of treating 3D worlds like the web treats documents. Make a world, host it on your server, and place portals (links) to other worlds hosted by other people. VRChat and similar have interconnected user worlds, but it's still all under one host, tied to one engine, behind a proprietary game - opposed to an open standard.

There's good progress like W3C/Mozilla/etc.'s work on WebGPU, allowing fast GPU access for untrusted content, which I'd consider a prerequisite. The fact that some non-technical brands sold some overpriced digital items on existing kids' games, then got bored and left, has little relevance to the actual idea to me.