Hi there ! I'm so happy my first book is now something real, in (recycled) paper ! When I got my first contact with the printing house, they asked me a PDF with crop marks and bleed. I had to move from Scrivener to Pages (macOS), and tried Indesign. I looked into Scrivener, and I'm surprise you didn't implement an option in the Compile module that make a PDF with crop marks and bleed, ready to send to the printing house. In my head it seems to be something pretty easy with few options/values to set and hop, it's ready !
Oh well, thanks Keith for your answer ! Maybe with the increasing amount of writers who self-publish you'll get some clues about this point. Anyway, many professionnal printers ask a PDF with cut marks and there are apps and websites that can flash PDFs to add them so, there's no urge.
Oh, and, I'm learning MMD and LaTeX with Scrivener and, the more I use Scrivener 3, the more I love it. The more I love it, the more I love you. Many thanks to you, your work is truly brilliant !
It's not as easy as it sounds to add, as the locations of crop marks and bleed dimensions depend on the characteristics of the printer. That means that Scrivener needs to provide a mechanism for entering details from the printer's spec sheet, and then needs to be able to apply that information to the output PDF.
It's fundamentally a layout/design task, not a writing task, and therefore outside of Scrivener's scope.
My opinion differs from yours, if Scrivener allows to modify the margins and the size of the police (it's some design stuff isn't it ?) during the compile, we can imagine this software does the whole job by adding two small lines at each corner (cut marks just need one information, "x millimeters" from the edges....)