Scala software engineers are some of the best paid out there.
What are the examples? There is no requirement for specific domain experience?
Well, I was hired into dev at a quant finance shop (you may draw your own inferences about pay), using F#, with no experience of quant finance.
Niche. Wouldn't be surprised if it's G-Research or Jane Street or one of those very few places.
Could you give an example of something that's not niche? If quant finance is niche, it's quite a big niche.
I don't know whether this is true or not, but either way, working with Haskell makes my job more enjoyable than if I was writing some other language anyway.