However, they will not replace Go for a rather simple reason. Erlang is an application runtime first and a language second. It's not meant to play with the native OS all that well, instead relying on its own scheduling, semantics, process constructs and the OTP framework. It exports a minimum set of OS libs for things like file system interaction, but you wouldn't write a Unix subsystem daemon in it. Though, you certainly can - if you want to hack with NIFs, port drivers and C nodes. But then you put the global VM state at risk if some native caller blows up.
For this reason, Go will remain a dominant choice for infrastructure and systems programmers. It definitely is replacing C/C++ for lots of things above kernel space, contrary to your statement.
I'd honestly dispute the characterization that Elixir is a small language. Erlang is easier to fit into your head, not least of which is because of how essential pattern matching on tuples and lists is. It's a consistent and homoiconic design, more warty constructs like records aside.
Finally, Erlang/Elixir aren't Unix-y at all. Don't get me wrong, BEAM is a wonderful piece of engineering. But it's very well known for being opinionated and not interacting with the host environment well. This reflects its embedded heritage. For example, the Erlang VM has its own global signal handlers, which means processes themselves can't handle signals locally unless they talk to an external port driver.