I don't think so. The forum is barely active here--and we're in, what, 24 time zones? A discord server would reflect that level of activity. I think several people have tried to get something going over at the Garden and the MCForum, but it never seems to go anywhere. I recall hearing offhand that there *is* an active MC chat service "somewhere", but I've never located or logged in to it.
I think the idea is that with the way things are going, Discord would encourage more involvement than a forum.
Back in the dark ages, for about 15 years, I ran a computer bulletin board--a dial-up BBS. Over time, the BBS sysop community learned a lot about what makes an online forum work. We picked some of this up ourselves, and some from the active usenet managers as well.
This forum ignores the most basic principle of generating an actively-commenting community: it has far too many topic areas.
Choosing the "right number" of topic areas is hard, but the basic principle is to have the ratio of topics to posters small enough that it's reasonable for a discussion to take off, but for the threads to be short enough that a regular visitor, e.g. 2-4x/week, isn't overwhelmed by volume in the areas they follow. If every topic doesn't see 2-3 posts per day, that topic should generally be merged into another, excepting administrative topics. While I understand Daphne's decision to have one topic per active story, I can pretty much guarantee that discussions will not bloom for any length of time in that structure. I would have set the forum up with a small number of topics (e.g. "coming soon", "general discussion", and some administrative ones), and then monitored for traffic, subdividing as necessary to meet a maximum traffic level per topic (e.g. less than 20-30 messages/day). When a topic begins to die off, it should be merged with another, to keep the conversation going. Typically that happens when a topic hasn't seen any traffic for a while--say, a month.
So: a discord channel is "adding another topic", and though it has some nice additional features, it just dilutes the conversation more. I don't think it's very likely that it will take off.