FWIW, I would love to add a core dev Discord server to my long-ish list of Discord servers. It's a chat platform I find convenient (much more so than Zulip and Slack, and slightly more so than IRC), very organised, with good moderation tools (better than Slack and IRC), and widely adopted. If people prefer other platforms I will endeavour to participate, but it won't be as convenient to me as Discord.
Huge +1. I'd love to have a place to hang out and voice chat (or text) with others on the core team in real time. I think it would double as a great social outlet, and we could keep it very simple to the point where its basically just IRC with some extra features. Using existing servers like PySlackers or Python Discord aren't ideal options (as much as I love Python Discord), just because there's too much noise to filter out if one is only interested in the core dev aspect. Whatever we do, I think it needs to be just for the core development community with as little noise as possible.