I'm not planning to join because I don't code (though I'm happy to join a channel if you get to a stage where end user or design process feedback is useful) but I would note that asking people to adopt new platforms 'just because they are open source', rather than ones that are used by a lot of people/ a lot of people are already familiar with, is pretty daft when your ultimate goal is to benefit the open source community through the work the channel fosters. 

As far as I know, for this type of work, Slack is the go to for most devs. The Foundation use it without issue.