Just a thought, but isn't the <meta> tag generally about Metadata, and I think from what most people are saying it's disregarded by most, if not all browsers. So isn't it's purpose then to just add metadata to the document and not provide ANY processing instructions to the parser (be it a browser or not), and thus shouldn't it then stay as "application/xhtml+xml" so it is accurate metadata?
Just my thoughts on the issue at hand.
-Brian