I'd normally not comment on stuff in the EE community list like this, but feel compelled to this time. And, Emily, it's equally applicable to the ongoing MP community discussions :-).
Context: ~30 year Apache contributor/member. You might have heard of Tomcat, Struts, Commons, and a few other things I have been involved in. Nearly all of my active time was before Slack et. al. were a thing. Email was/is king. If you peruse the archives of these lists, you will see *thousands* of comments/responses/help from me.
Problem: Whenever your community divides channels of communications across more than one solution, some people inevitably get left out - not necessarily from everything, but perhaps from "significant" discussions on alternative channels. Nobody has time to cover everything -- as we have seen from lots of comments, many people who would like to be part of the community, but can barely keep up with the email flow. I was incredibly fortunate to (at the time) work for an employer (Sun) that actively encouraged my connections to the OSS world. Not everyone has that luxury.
Solution: Keep a single (IMYO email) channel as the single "official" discussion forum for a community. May be old, but have you contemplated what an IM channel means to a worldwide audience? Been there, done that, with teams on the West Coast of US (PT), all of Europe, Russia, India -- there's no possible time of day to get everyone together (or anyone together if you are spread globally) synchronously! Give up on that goal, and you find that email actually works pretty well, ... once people get used to how to use it (you want to see bad examples of "use it"? Go to random slack/IRC/Instagram/Twitter (shudder) channels).
(Re)learn to be patient.
Historical Note: My wife (PT US) corresponded with an exchange student from Nigeria while she was a student here. When my kids were in grade school, a teacher was pretty excited to share cultural insights -- maybe we could establish pen pal relationships? Great idea, except that the average time to deliver mail was 3-6 *months*, with no guarantees. The world now is a different place.
Caveat: You do need to give up on expecting instantaneous response to your questions.
Benefit: You get to hear what everyone in your community, all over the world, has to say. (Leads to the "English only" question, but that's not my issue here).
Benefit: Most serious discussion email lists are archived and indexed, so they provide a historical resource for people trying to catch up on what has happened before.
Problem Example: Cord cutting. Yay! I don't need to be beholden to a single vendor! Boo! I need to sign up for three/four/five/??? subscriptions even to get what I had before, let alone everything new I might like!
Craig McClanahan