Indeed, it's hard to find a new car without a CD player, but there's an increasing aftermarket push coming from XM and Sirius satellite radio as well as the legions of iPod owners who want in-car integration.

Long term, I expect that Bluetooth is going to be the answer. It's got plenty of bandwidth (at least for MP3 files, although pushing a 1.5Mb uncompressed audio stream might be an issue), and it's already gaining support for cel phone integration. You could certainly imagine a standards body including MP3 makers, satellite radio people, cel phone people, and heaven knows who else, defining such a standard. Then, you'd get aftermarket people coming up with integration kits, and so forth.

Hopefully...