Very nice feature set! I especially like the referencing functionality and ToC. Though I wasn't able to test it out (stuck with Windows at work), here's some feedback:

In the example images, you write that you eliminated all toolbars - this is arguably false since I see a vertical one on the very left ;-). I would even get rid of this one and move the ToC to the left edge of the window. You can keep the help button (move it next to the MacOS window controls) and maybe even the export button (also next to window controls) but I'd rather make use of the system UX and use the MacOS toolbar instead (same for the preferences button, it's useless if you make use of the OS functionality).

I'd love to give this to my coworkers for their Wiki drafting, right now I have too many issues with people copying from Word and the system trying to do ... something with that input. Unfortunately, only Windows flies here ...