I am not sure that we can call a text that has not yet been typeset a "book". In any case, do you know any such format that does not completely botch equations? The closest I can imagine is html with mathjax.
One of the problems with including mathematical formulae in a reflowable document format is that the concept of reflowable mathematical notation simply doesn't seem to exist, so In practice you'll end up with something equivalent to a picture.