HTML is the answer, it is future proof, it is 100% portable.
Now we need a solution to move all ebook formats to html.
Now we need a solution to move all ebook formats to html.
If not, we're not doing the right thing.
I insist, html is the answer.
XHTML maybe? Some XML dialect? I can see these working if the toolchain (generators, interpreters, transformers) is tightly controlled or harshly forces compliance. Even still, I'd like my books to always look correct even if made by Microsoft eBook Publisher 2013.
Layout failure on the web is a minor annoyance. Layout failure for a e-book I paid $20 for is completely unacceptable.