Brett on 27 Dec, 2017 04:14 PM
Ulysses is able to provide the live preview because they generate their PDF output completely from scratch. Marked uses the macOS print/PDF system, which doesn't generate the pages until export. In order to provide a live preview with the current system, I'd basically have to be printing the document repeatedly on every update, and even in the background that would be problematic.
I do intend to revise the PDF generation strategy, but at this time the only way to see the final output is to actually create the PDF (or use Print->Open in Preview).