What are the possibilities for somebody that's pretty heavy iOS senior to transfer to a role building applications or services in Rust (or Elixir, for that matter)?
Of course, that's just one anecdotal example, but I'd encourage you, dep_b, to look for openings. I'd guess that only very few companies use Rust exclusively right now, because of its relatively young age and because it frankly doesn't make sense everywhere, but many use another main language plus Rust.
One had to make an active effort to pick Python to be a tool for the job.
I remember being in one of big government project pitch session and the project manager asked "What this Python language? Sounds like some toy."
Times will change. However Rust sweet spot is system programming. Even though one could build e.g. websites with it, Rust loses its edge and becomes verbose, a too heavy hammer.
OneSignal (SFBA) and Sentry (SF, Austria) use Rust. I was actually surprised half a year ago when I started looking for companies using Rust that there were many more than I expected.
Rust, on the other hand, has a lot of momentum behind it in the embedded space. Bare metal and embedded RTOS options.
Rust is slowly gaining momentum. Jobs are starting to pop up here and there.