Only thing that stops me using DT’s Markdown editor is the lack of style options. Which means that there is not enough white space for my taste, which has become used to the text presentation I can get in Ulysses or iA Writer.
If I could adjust line and para spacing, page margins, and have a centralised column of text in full screen view, I may not every leave Devonthink either. Editing in an external editor works well, however.