Multi-processing is an orthogonal issue to single-threaded JS. The same asynchronous logic used to have multiple browser engines with multiple JS runtimes talk

Multi-processing is an orthogonal issue to single-threaded JS. The same asynchronous logic used to have multiple browser engines with multiple JS runtimes talk to each other could also be used for multi-threading while making shared, thread-safe datastructures of non-JS parts much easier.