HackerNews may not be the best place to sample for UML usage. It consists mainly of two communities that have a bias against formal engineering methodologies in the development of software.
I won't comment on the pros and cons of UML. Instead I'll invite you to ask yourself a couple of questions.
1. What other clients do you support who have similar characteristics as this client (and may therefore also benefit from UML support)? If the number is significant in terms of impact to your bottom line versus the time you'd have to spend implementing it, then you should consider it worth your time, and view it as an opportunity to up-sell (if you can) or keep existing customers.
2. Do you intend to attempt to move into supporting large enterprise, and especially government contractors? If so, you might consider UML support just because it is ubiquitous there.
Mainly the group that thinks of everything in terms of the mathematics of CS, and the group who thinks in terms primarily of "just ship, ship, ship code 'pragmatists'."
It isn't really divided by front end versus back end or the like.
I presume you mean the Haskell crowd? The Lisp crowd is more about expression rather than "correctness" and rigidity. FP doesn't really have a formal definition.
> trying to evangelize the world of programming to do things one way; their way.
I think the world of computing is shifting towards a lot of async work, and if you've ever written large threaded apps, having too much state becomes the greatest of burdens. Clojure, for example, minimizes state and uses Software Transactional Memory to manage mutability.
I won't comment on the pros and cons of UML. Instead I'll invite you to ask yourself a couple of questions.
1. What other clients do you support who have similar characteristics as this client (and may therefore also benefit from UML support)? If the number is significant in terms of impact to your bottom line versus the time you'd have to spend implementing it, then you should consider it worth your time, and view it as an opportunity to up-sell (if you can) or keep existing customers.
2. Do you intend to attempt to move into supporting large enterprise, and especially government contractors? If so, you might consider UML support just because it is ubiquitous there.