I think going one-step further and making LaTeX the entire backing structure of a document would be a great idea. Kind of like HTML WYSIWYG designer tools. Would be a boon for interoperability which is probably why it'll never happen.
Latex can't produce HTML, it can't produce EPUBs or any other reflowable document type. It can't produce any document which is accessible to blind people (other than giving them the raw LaTeX file).
Note: You will find various libraries that claim to produce HTML output. I can tell you from experience none of them work, given a random LaTeX paper you download from, say, Arxiv.
The assertion was that LaTeX cannot generate specific formats. Using Pandoc (NB: Pandoc Is Not Markdown, though it's often used with it), s well as earlier tools, that is in fact quite possible.
Using templates, with quite a level of flexibility.
