The only thing I read was very vague. No details about what the changes are and whether it would be a "patch", an add on for Vista Ultimate or a sepearte product.
The only thing that was certain was that it won't be this year.
No, when I last spoke with the Media Center team, I was told that Microsoft shipped a Media Center update every year around the holiday season and they would try to keep doing that. At the time, SP1 was expected by late 2007, so the delivery schedule made sense. Right now, it's unclear if the Media Center update will ship out of band by itself to Vista users this year or as part of a set of related updates (like "XP Reloaded" from 2005) later on. What is clear is that it will not ship as part of SP1.