Fundamentally what I think we want to do is build the primitives you would need to create your own fanout. That means we need the ability to push events to Worker nodes, and for Workers to be able to terminate WebSockets for you.

If you can accept up to 10s of latency, I agree that KV could solve the 'pushing events' problem for you. (A tuple store is semantically equivalent to message passing, and it will get easier when we support range queries).