What about using some subset of DIVs from HTML so that HTML Editors could be used to generate PDF templates?

Do you mean WYSIWYG HTML editors?

The problem I see with this is that HTML DIVs are useless without CSS, which is where things get really messy. It is also worth mentioning that PDFs are very "page" centric, and those pages are of a constrained size, which doesn't match well with HTML and it's "take up as much space as needed" layout approach. Having written plenty of PDF "pagination" code, I know this can be trickier than it seems, and is not always easy to generalize.