That's an excellent point about Tcl; I'm sure it was a strong influence on Brendan's design for JS, though maybe not as strong as Perl, Java, and Scheme.
We clearly need some way to take advantage of manycore, but
I'm still not convinced that threading with implicitly shared mutable state is the right default. It isn't even what the hardware implements! Every core has its own cache! It's a better fit to the hardware than a single giant single-threaded event loop is, and I think that accounts for its curent dominance, but there are a lot of other possibilities out there, like transactional memory, explicit asynchronous message-passing interfaces, or (similarly) lots of tiny single-threaded event loops like Erlang (or, maybe, like Web Workers).
We clearly need some way to take advantage of manycore, but I'm still not convinced that threading with implicitly shared mutable state is the right default. It isn't even what the hardware implements! Every core has its own cache! It's a better fit to the hardware than a single giant single-threaded event loop is, and I think that accounts for its curent dominance, but there are a lot of other possibilities out there, like transactional memory, explicit asynchronous message-passing interfaces, or (similarly) lots of tiny single-threaded event loops like Erlang (or, maybe, like Web Workers).