The labs page says the following:
Atlassian Editor beta
The new editor provides a new visual refresh and rich content editing experience. This editor is used in comments and pull requests. Look out for the editor coming soon to other Atlassian products near you!
Is my understanding is that Atlassian Editor will become the only option at some point correct? If yes, it will be a significant regression to me and many users, as without an option to edit the underlying Markdown markup it's very difficult to correct mistakes — and for many people, or, in fact, most people knowing Markdown, directly typing the markup is much more productive than playing with buttons and menus of the WYSIWYG editor.
I’m certain removing the Markdown editor will force many users to reconsider their choice of the platform, and even possibly migrate to GitHub (as Mercurial is now a third-class citizen here anyway).