I second pandoc. I managed to get a book published with sources in markdown. And I can confirm that you can run from latex, but you cannot escape it.. Before you are done, your markdown will typically end up moving through latex2pdf. I think what nailed me down was proper page numbers. They are one of a thousand small things you expect to be "right" in a book, but nevertheless only latex seems properly prepared to handle..

And as others have said, the marketing/community for a book is a full extra job, separate from being a writer.