using z.m.l. -- or r.s.t. for that matter -- i can churn out an .html file which knocks the socks off anything you do, and i can also churn out a .pdf that looks very _beautiful_ (or "pretty", if you prefer, both words apply fine, thanks.)
The simple answer to "I can do it" is to actually show that you can do it, but everything I see "churned out" is butt ugly -- and then excuses are made. Once you can make something "pretty" using your own tools and books of your own creation, then put your tools online so that those of us who actually make books can put the proposed tools to the test -- except that the tools WON'T work, as anyone who has created books for PG can already tell you. Even simple books have too many exceptions to the rule for pretty printers to work, as K&R already discovered over 30 years ago. HTML is far from perfect for PG needs, but it can be made to work, as 10s of thousands of HTML formatted books for PG already attest -- as does the preference from real users to download HTML or one of its derived formats. Or, better yet, put up some ZML or RST test files on the PG website and count on your fingers and toes how many customers you actually get for your newly invented file formats! Good luck on that one! The idea that end customers want to run your tools to generate their own book formats is ludicrous. They want to put an ebook on their ebook reader and read it, period, end of story. And not be faced with ugliness from PG or any other vendor. That's the whole point of ebooks -- a black box encapsulated lump of goodness which you do not have to muck with! Some ebooks from PG and other places pass this test -- and others don't.