Our biggest struggle is with support within our community. Helping someone is nice, but odds are that someone else has the same question and losing their mind with Google. Mattermost does not provide a good way to archive topics. We push people to use our Gitlab or Stack Exchange for support, but both are hostile in their own way (not newbie-frienfly). Anyways, something there might do wonders. Maybe some kind of tool that lists popular threads on a public page?
Another wishlist would be to be able to hide or block people. While we do our best to be friendly, there are just some people that I get really annoyed when they PM me, and some others that I just don't want to see their comments in public channels (kind of like hidden tweets that you have to click to show them).