Just a thought,
The idea of a media mac is a good one, but I don't think it fits with the content delivery plans of Apple.
When Apple first came out with the iPod, there wasn't much content for it, being that iTunes was in a infantile state. Then when iTunes became more robust in its offering of content the iPod was becoming more useful, as well as the content for you to have on your Mac. But iTunes nor the iPod isn't just for Mac, it's also cross platform in nature, so is the content. When Adam suggested that the update for Airtunes is overdue, that makes much more sense that Apple would love nothing more than to offer a product that can be used not just by current Mac owners, but also PC owners.
So if a wireless iBox that can recieve content, either video or music, to be played on a TV, offered to work for either Mac or PC is a much larger market share than just offering a Mac to plug into a TV. Content secured via iTunes of course.
Also offering a wireless iPod to work with this device would be a nice compliment as well.
So I suggest no media mac, but a wireless receiver for video/audio, with interface with an iPod.
This could in someway be the link to the so called "Asteroid" rumor way back when.