I think there's a battle between nerds and non-nerds, and maybe in between is the worst place to land. I know some of my projects' users complain a lot about the lack of a WYSIWYG editor in our forums and issue tracker (we use Markdown, displayed plain until previewed or saved). Some people hate it. But I would hate a standard WYSIWYG editor, so we just accept the hate. Every Markdown-ish WYSIWYG editor I've tried has sucked...so I don't know that it actually is easy to get right (if it is even possible, where is the good example?).

Slack serves a mix of nerds and non-nerds, with non-nerds becoming a bigger and bigger portion of their user base over time. I can only assume it will become less and less enjoyable for nerds in service to the goal of serving their growing non-nerd users. For my own projects, I don't foresee myself ever using Slack (I use it for work). It feels like a decent product getting worse with time as it tries to be all things to all people.