I know that you have already squashed the idea of implementing a lightweight markup language like Markdown as a first class citizen in the Rich Text Editor implementation of TinyMCE you use in Aha! (found out with a simple class check in Chrome).
For those users who want to quickly add headings and other basic syntax markup as they type, you could consider implementing the https://www.tinymce.com/docs/plugins/textpattern/ plugin and define a list of Markdown-like keyboard shortcuts that would be converted in the TinyMCE backend to text.
I rarely rate a feature as "Yesterday" but I'm continually frustrated by the TinyMCE editing experience in Aha. For a Tech Writer that has moved into Product Owner responsibilities, the WYSIWYG experience is always sub-par. Add to this the lack of keyboard mapped shortcuts and you have an editing experience that is frustrating more than it is excellent.