James, I have zero problem with a very limited WYSIWYG that offers only the most basic semantic HTML markup: headings, ordered and numbered lists, bold and italic, etc. From an ease-of-use perspective, that makes more sense for content creators, and there should be no difficultly in converting and parsing those tags.
Even that, however, does raise issues of whether the tag is used for styling or semantics. Why bother trying to communicate the difference between italics and emphasis to content creators, if every major browser renders <em> as italics? Well, what happens when speech interfaces are mainstream, and emphasis has a different vocal cue? A lot of shouty book titles, perhaps.
I think the *really* interesting future is figuring out what should be represented with a field and what should be represented with custom markup in the editor that define what something is.
I storified a little rant from @eaton on this topic: http://storify.com/karenmcgrane/wysiwyg-as-editor-for-rich-data-types