Check out renderfarm.js from resources. It’s still quite far from what you need right now but a step in that direction.
I think the most time consuming part in the pipeline is still the ray traced rendering needed for the real HQ graphics. But that’s been getting better year on year and feels this might be doable in the not too distant future.
Check out Lumion. It’s a desktop rendering software used widely in architecture and landscape which does a pretty neat looking real-time render. Unity has real-time raytracing in their preview already. Enscape is another one with nice realtime graphics.
Then comes the part of sending it to the client. If one was to send diffed pixel buffers across the wire something like WebRTC or sockets might do the job. They’re already used pretty commonly for videos.
Sorry to be the optimist here, but this is pretty exciting. 