It's hard (not impossible) to make it work in principle because a printing press doesn't need to infer meaning from the post script or whatever you provide it. A browser does need to, so you'd need to layer the extra semantics on top of your WYSIWYG editor.
Which means asking questions like "this is 36 pixels high: is it a heading,; or is this just a landing page with big text?" etc. So maybe I lack imagination, but I don't see it being that easy a problem to solve from a UI point of view.
There are plenty of semantics in InDesign documents. InDesign is all about character, paragraph, list and table styles – it’s what you use to make InDesign work. You wouldn’t have to add much to make those styles do all the semantic work.
Yeah, you would still be able to just ignore all that – just like you can adjust each headline individually in InDesign – but that would only mean that you are an incompetent user of the software. A good WYSIWYG editor wouldn’t always have to produce great markup but a competent user of the software should be able to easily make it produce great markup.
I’m really not that sure why adding a GUI for semantics would be so hard, especially since existing concepts like paragraph or list styles already map very well to HTML concepts.
Which means asking questions like "this is 36 pixels high: is it a heading,; or is this just a landing page with big text?" etc. So maybe I lack imagination, but I don't see it being that easy a problem to solve from a UI point of view.