Agreed, backend isn't going to disappear. I was thinking of learning go, but going for Elixir seems like it might be a better option - happy to have read this.

I don't think ruby/rails is going anywhere for a while though, it's too easy to get things up and running. And I think node is going to be around for a while too, and increased familiarity with javascript is pretty much guaranteed to be helpful, so going that direction isn't a bad idea either.