If Discord tacks on a layer of forum-like discussions besides the chat... It might take over a chunk of current reddit-focused communities.
At least for me, personally, that would supply the only thing I still use Reddit for, some of my hobbies have communities on Reddit + Discord and I participate in both, if Discord provided a discussion board to allow a more asynchronous communication I would ditch Reddit completely.
It seems to have something like this. I'm in the CloudFlare community Discord and there seem to be some channels which are message boards. Crappy message boards, though. Just like Slack with threads, I haven't seen evidence of a chat platform adding meaningful async communication that doesn't feel tacked-on.
At least for me, personally, that would supply the only thing I still use Reddit for, some of my hobbies have communities on Reddit + Discord and I participate in both, if Discord provided a discussion board to allow a more asynchronous communication I would ditch Reddit completely.