They're all wonderful, established technologies and all very capable of making concurrency relatively painless. At this stage, you should go with whatever you would be most productive in: do you already know one of the languages? If so, go with that one (always be shipping!). If not, how much do you like the syntax of each? How much do you rely on static types? How mature are the third-party libraries you're going to be relying on?

I've been building software using the exact stack described in the linked article for the last three years. I don't think about my backend very much, it mostly just works. Most of the work is on the front end. Elixir/Phoenix/Absinthe have been almost completely frustration-free. I'm sure Rust and Kotlin are great too.