Every time this comes up, I feel compelled to point out that true WYSIWYG has to work with all parser tag extensions. Otherwise, it's not really WYSIWYG.
Not to mention, it puts all of the presentation logic in the article which eliminates the benefits of using CSS. I'd much prefer a Content Editor that is WDYGITDYG (What Data You Give Is The Data You Get) - much like Semantic MediaWiki Forms does.
Mark W.