Scott M. Fulton, III on the design potential of embracing HTML5:
HTML5 offers a glimpse of the freedom to define the Web publication the way it should have been defined fifteen years ago: as a more functional descendant of the magazine and the broadcast. But it can only do so to the extent that the content management systems upon which publishers have entrusted their livelihoods embrace, incorporate, and advance that vision. This is not a certainty; in fact, I fear it's not even a likelihood. The CMS of today is a machine that produces blogs - that shapes and forms content to fit in equal-sized nuggets dropped onto a conveyor belt, the length of which constitutes the breadth of their natural lives. It's about as prepared to embrace the full prospect of HTML5 as government is prepared to embrace "change."
At the risk of sounding like a fanboy, I think ExpressionEngine could do a fair job of realizing Fulton’s vision. That being said, I’ve recently begun thinking about a return to the pre-CMS model of web publishing, using hand-crafted static HTML5 and CSS3 for layout publication. Not for Opus, mind you, but for other things.