case in point, I built my startup in elixir. completely agree on the difficulty in hiring but its not hard to teach. It was harder for me to find people who knew sql well. Unlike active record, ecto embraces sql so you have to know sql to use it.
anyways, its time will come. more and more companies are adopting it from discord to supabase to <cringe> trump media group.</cringe>
Also, I think you underestimate how many people (such as myself) who use Ruby in a very functional way already. Immutability is really not all that different. The only thing is you can't use ! methods and instead have to assign. For example instead of `array.sort!()` it's `array = array.sort()`. It's really not that hard, and in fact I found it easier because I didn't have to remember if `array.concat()` mutated or not.
IMHO the only "hard" things for a rubyist to learn are pattern matching and Actor model (OTP) concepts. Actor model concurrency is definitely different. But for an experienced programmer, that can be learned in a couple of hours (or less).
I say this as a massive Elixir and functional programming fanboy.