I don’t think it is extreme. Imagine this is added to WebKit. Now I have a new question to answer - can I use library X across multiple threads? How do I know it does not have a little cache inside which breaks if I call it from multiple threads?

Another issue is lack of memory model (sorry if ai missed it) which means memory updates will be published to threads differently on different architectures.

And then an obvious problem of mixing async with locks - never ends good.