not speaking in any official capacity, but: we great internal training material courtesy of some very thoughtful folks, and ultimately one hopes that most of the code is going to be pretty straightforward wherever possible.
There are two countervailing effects when you choose a more theoretically advanced programming language. On the one hand, your hiring pool shrinks. On the other hand, the quality of the remaining hiring pool goes way up, which acts as an excellent recruiting filter (for both employer and employee). Jane Street made a similar play with OCaml.
The problem is that the intersection between your business's interests and the interests of the small pool of available developers is usually very small.
Building banking apps? Well, even if it's Haskell, the Haskellers were dreaming of GPU compiler jobs, not banking front ends. So you're probably down to literally 5 qualified people on earth who want your job.
But then 3 of those 5 don't want to relocate or have other operational desires that require you to re-think how you run your team, and 2 of those 5 believe so strongly in supply-demand that their salary should be 3x the industry average.
Many companies, including Jane Street, come to the same conclusion: If you really want developers of a niche language, you have to be very good at finding smart people who don't know the language and training them.
The article has a section covering this. According to them, finding Haskell talent is not difficult, the bigger problem is onboarding them into the company coding style because Haskell developers come with strong opinions.