Whatever master format you use it should do two things adequately preserve the original layout, and be able to be converted to the formats acceptable by the devices available today and the future.
Those who have tried it find these are mutually exclusive goals. How to format something as simple as a "Dear John" letter found within a book becomes dependent on the width of the target class of devices. Wide devices need ways to use up that width or they look stupid. Narrow devices need ways to fit it all in or they look stupid. Formatting and display of information within tables is another, and more severe example of the difficulties we run into. And some very simple things simply "look" different on paper and on electronic devices, leading to different design choices, such as choice of font, and choice of paragraph formatting -- indent looks better on paper, whereas line-between (as Mr. Hart chose) looks better on electronic devices. And the format choices we have to work with today do not understand, nor support, the need to deal with these issues "automatically."