Again, I believe some are trying to do an apples to apples comparison with Discourse and mailing list technologies.  Discourse was build from the ground up with the goal of fostering communication and collaboration.  Hyperkitty is a bolt on HTML to mailing list archives.  It's good for what it is, but it isn't Discourse - and usage numbers tend to bear that out. 

The fact is that email usage is declining.  People are moving away from it and prefer to use other platforms for collaboration.  As with many things... when something new comes out, there are a group of people who push back and want things to stay as they are - history has proven time and time again, that change is inevitable.  If something new is the better solution, as people become aware of it and use it - it will become the go to solution.  The examples are endless and span multiple disciplines. 

Fedora has a long history of supporting new and innovative solutions and toolsets.  That is what helps differentiate us as a distribution.  We need a tool that will encourage more participation.  I believe Discourse will help with this - people will discover new and more efficient ways to do their work and the sun will rise the next day.