This is more of a question for other open source developers. I recognize there are payment structures in the Mac App Store that do not work for paid software. However, I’ve always wondered why other open source apps do not publish there.
My general experience publishing Monal there has only been positive. While I still push out beta clients on the web the App Store has been the primary way that users have discovered Monal. It also takes care of several things that are pain points for developers such as upgrades and hosting/bandwidth costs. I honestly think more people use XMPP because I have made the software readily available in a trusted location. The Mac App Store has a lot of good software but also a lot of junk. The ratio is a lot worse than on iOS and I think we should change that.
If the problem is the $99 developer fee, would you be more interested in publishing software there if it were to go away (or at least not be something you need to worry about)?