Looks useful! Two things:

1) How do I make several levels of headers (#, ##, ###, ####)? This is what I use markdown for the most - nesting texts in clearly visible subsections. In the menu I can only see only one header, and in the screenshot I see two (==== and ---).

2) Rendering the PDF side-by-side would be useful. If I understood correctly one currently has to compile to PDF manually, which sort of defeats the purpose of a GUI app.