Added a button, not included by default but can be added from the admin dashboard. Used a fancy pen icon, not sure if there's a better one. Note that retaining cursor position and undo history when switching editor types is impossible. I've updated the preview.
ornanovitch another issue: when I click on the emoji or mention control, I have to type a letter to display the dropdown. When I type : or @, it is displayed directly.
Fixed
At this point, I think the editor is pretty much feature complete for its initial release. That being said, if I missed anything, I'm open to suggestions!