1. Don't be Slack / Teams :)
What I mean by this is if you support it, support it correctly rather than "markdown as keyboard shortcuts" that some products do where if you make the simplest of editing changes, your "markdown" isn't recognized.
2. Devs want to consistently use Markdown across their entire suite
At my last job, we were switching to Azure DevOps. They support Markdown in the developer workflow (PRs) but rich-text-only for Tasks (to be non-dev friendly?).
At my current job, I'm involved in developer productivity and have been interviewing people to collect input for where we want to take development. We currently use Phabricator which uses Remarkup. This is a source of frustration because its not quite the markdown they use everywhere else.
From these, I'm thinking Markdown Pages would be the top choice since it allows developer-only interactions and marketing-only interactions to stay within what they are comfortable with,
on (2) -> it sounded like you're saying (a) 'across entire suite identically is good', but that also (b) 'if there's a clear separation of Dev vs nonDev apps/docs, having different support is okay', did I read that right? please correct me if wrong.
In my personal opinion, Atlassian's rich text editor (or, seemingly, the 4-6 different one's you guys have built) is unforgivably terrible, so true markdown is the way to go if having both isn't an option.
The "reasonable subset of Markdown" is also a very useful specific detail, exactly the kind of specificity that helps us do our jobs.
It is so frustrating to have to remember to use double-curlies for inline code/pre sometimes, and backticks other times. In each case, the other doesn't work. More than once using one has resulted it rendering correctly on the immediate page but not on the next.
This is one I encounter regularly but is far from the only inconsistency in support.
1) markdown macro (limits markdown to the body content, and not interacting with other macros or styling)
2) copy/paste markdown -> autoconvert to WYSIWYG (limits markdown to copy/pasting, so no editing Markdown inside)
3) "markdown pages" (something like 'this page is Markdown only, no WYSIWYG)
I make no comments/promises on any of these becoming real but looking for what's most valuable