Disappointingly to some of us, it seems the general community has agreed to shift from Slack to Discord recently (as can now be seen on the official org website) which kind of closes this thread.
I did however just catch this though in the Haskell community:
Welcome to haskell.social, a constellation of haskell-adjacent, social fediverse nodes.
With PureScript being Haskell-adjacent, the admin maybe would be welcoming of the PureScript community – especially being fresh and not having many users 
(though the domain name is clearly “haskell”). At any rate, it could be a project worth watching to see if the uptake, moderation, and maintenance of various federated services (Pleroma (microblogging) and Matrix (chat)) isn’t too bad for self-hosting.