That's the thing that is missing in discussions around many languages. You can't just add multicore or actors to a language post-factum. Because by the time you get around to doing it everything in your language, from standard lib to third-party packages, has already been written with no concept of multi-anything.
And still, time and again, languages are being designed with these concerns as an afterthought.
Is that still happening? My impression is that any languages designed since multicore became common have thought very hard about their approach. The problem we have is that a lot of our languages have been around a while. Even Python is 30 years old at this point!
Erlang here is the miracle to me. Its programming model was designed for concurrency on a single core, but when SMP processers appeared all it needed was a VM change that was completely transparent to the programs above it and suddenly all Erlang programs were extremely parallel!
