I tried out and one issue I had was with indented paragraphs. I ended up using LibreWriter's regex search replace to remove all the extraneous newlines.
I only gave it a try for a chapter or two just to get a feel for what might be involved. I first tried pandoc. This mostly worked, except for the indentation of paragraphs. I took care of that by setting up LibreOffice's paragraph indentation, and used LibreOffice's search replace to remove the (now) extraneous new lines.
My recommendation is to grab a decently long markdown document and give it a try.
