"The North" PW has separate UD areas that players can start in, explore and avoid sunlight for most of their existance. Arelith as you mentioned does as well. "EFU" used to, but I believe the present chapter of their campaign has moved to the surface. There's Amia (which is a split from Arelith) that has a dedicated UD area last I recall too.
Is there a "need" or a "void" to be filled by another choice of where to play in "the dark"? I'm unsure. I've had players on almost every PW I've been on (including my own) that asked for it. Its never been a majority though. While some might play duergar, kobolds, minotaurs, etc... , the two biggest draws to play in a UD setting always seem to be drow, followed by mindflayers (if allowed).
Despite what players may or may not desire, do you desire it? If you have hesitations, then you might find the task daunting and or unrewarding to take on. Don't let others persaude you to build/add something you yourself aren't 100% behind first.
'> Then use the old Field of Dreams addage if you do. "Build it and they'll come".
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