I would say that the strengths of Erlang have made their way into the mainstream, but into infrastructure and tooling rather than languages. I believe the reason for that is because the current crop of popular mainstream languages will never forsake their imperative roots. Erlang's true strength is that it approaches the distributed computing problem from first principles, which yields a language that feels right to work with in that domain; whereas the mainstream attempts to shoehorn distributed computing onto an imperative foundation, which has always been very awkward since it's really just trying to square a circle.