When the MP3 feature of the 05 HU was announced. I predicted that transplants of the 05 HU to earlier year cars would be the new rage. I personally can not see putting a funky white IPOD with a tiny unreadable screen in the car to play MP3's when you can have a neater, no clutter, covered by insurance official Mini HU that will play MP3's off a CD.
You can get about 12 full albums of music on a single CD in MP3 format, and thats encoded at 160 instead of 128. Also, it has been discovered that the 05 HU can "fast forward" through MP3 files, as well as skipping them all at once. The lack of radout is a hassle, but quite frankly, given the position of the radio, trying to read and drive at the same time is a hazard, anyway. Since you can skip or scan with the MFSW, you can still do a lot of navigation of the CD blind.
Let us know how it goes. If it turns out to be as simple as everyone expects - literally a plug-in deal, the value of the 05 HU will rise.