This is where I'm at right now and it works rather well. I have a glue script that automates some shorthand in the Markdown into LaTeX for PDF and pre-set styles for DOCX and HTML exports. It works rather well, and being able to tweak my own LaTeX shell for the content is quite nice as well.

It's ePub that gets the weak treatment right now. Which just has me wondering if I can have my tool output the input files this standardebook toolkit wants (probably) and get a reasonable output from it.