It seems like your idea is that by creating a highly restrictive format (forbidding things like <div>), it will force publishers to create books "the right way"—"the right way" in your mind being heavily marked-up, style-less content that can be slotted into a general "books look like this" design shell, and one that is easily searched and indexed.
I don't think a restrictive format would accomplish this, because folks will always do things a little bit wrong. It's just the nature of being a person. The best we can hope for is to make things easier to do right than they are to do wrong—and if everyone's doing it wrong, we have to reassess what "right" means.
Personally, I would rather see semantically meaningless stuff like <div> than things that are semantically incorrect, like tagging dedications as acknowledgements or introductions as forewords, which is the sort of thing I think you'd see a lot of with the kind of tagging you're talking about. Especially considering that as it is, we already see a lot of p.normal and p.blockquote type stuff.
I also don't think that sort of exceptionally precise semantics adds much to the reading experience. People usually determine what they're reading by reading it.
I don't like the idea of taking even more control out of designers' hands either. I think perhaps you have very little love for the craft of designing a book, and it's flavoring your perspective on this. The idea that fonts, indents, dropcaps etc are "not essential" is kind of mindblowing to me, but I suppose that's a matter of taste and a difference in philosophy.
Semantics and hierarchy are important, but they are not the entirety of a design, and not all aspects of a creative work can be defined semantically.