Distributing the simulation is one thing. The real issue is the cost. Its no good to throw more CPUs at it when every CPU costs you a lot of money to rent in the cloud. Also, the bandwidth issues are real. I've spoken to these guys (Improbable tech) and they could not tell me if it was cost efficient. Also, since they run a full copy of Unity of the servers, that itself is very inefficient. They let Unity do all the physics work. But a full stack of Unity on a server is a hog for what it needs to do. So again, more $$$.
What they've done to distribute simulations is good work, not downplaying that accomplishment. But without a way of doing it economically its a big business problem and threatens making your "nut" every month to keep game going as a commercially viable thing.
Also, we don't use Unity and they don't support Unreal.
Edit: Final note. You have to rent your servers from Improbable, currently...so what is their incentive to keep it cost efficient?