During my Java days, I saw countless broken attempts at writing parallel code (typically only saved by the Java VM not exploiting all possibilities the spec allows for, such as only updating shared global state at the end of a synchronized block).
Along came NodeJS and proved to us lost java souls, that with non-blocking I/O, you don't need hundreds of threads to make performant code. In fact, one thread is enough, also for driving complex UI.
Now we're given wonderful new Atomics and SharedBuffer, I bet there will be an underlying expectation that to "keep up" you better start driving complex UI in multiple web workers, because, performance.
But the complexity of coding parallel stuff hasn't gone away. Atomics and Run To Completion functions isn't simple.
I would not be surprised if I'm two years from now am debugging broken attempts at writing parallel code in something like react-parallel.