BlogML. I'll Bite.
HTML isn't good enough. Here's a proposal for BlogML, an attempt to standardize a separation of design from content even further than the use of CSS. While I agree in principle with the idea, there are a few problems that spring immediately to mind.
First, the proposed use of the div tag's id element seems restrictive. How to solve that problem: new tags? That's just XML (or, to be more specific, XHTML); it's all been done.
Second, the very idea of a specified BlogML seems restrictive. For me, one of the great attractions of a blog is that it is anything I want it to be. It can or can't have comments, each entry may or may not have a title, timestamps are always optional, and who's to say that blogs need be chronological?
I don't want to dismiss the idea out of hand, because I think it holds promise. This does call for some heavy-duty discussion, though.