My understanding is that Erlang is still primarily used in the telco industry, as it's name implies. In general Erlang shines in doing most software that would run on a server for long periods of time when interruption is expensive (it includes the ability to hot-patch running processes, for example).
Use of a GC is problematic for soft real-time systems (interestingly enough, it can become useful again in hard-real-time systems but that's too long of a tangent here). In rust you can completely ignore the GC just by choosing to not use it. The ease of getting raw-pointer access in rust also indicates places it could be used (I feel like I could write a bare-metal application in a subset of rust with a lot less work than doing so en Erlang).
It used to be that resources were so constrained that the entire OS would be written in a combination of assembler, and something slightly higher level (most commonly C, other times a reduced set of sine other high-level language). This meant that those languages were system languages. Nowadays, writing all but the kernel and drivers in something much higher level has become feasible, so the term "systems language" has blurred in meaning.