The six-disc CD changer seems destined to join the 8-track tape player and the still-sometimes-seen cassette deck in dropping from car option checklists.
The CD player itself probably won't go away so quickly but it's becoming a data transfer mechanism in addition to a way of directly listening to store-bought CDs. Most new car CD players can read MP3 files stored on CDs. Many can also read DVDs. One DVD disc can hold about 25 to 30 albums worth of MP3 files.
But this still requires users to burn MP3 files onto CDs or DVDs. It would be easier to just let people play the music they already have on their portable MP3 players or at least carry the music in a way that requires less effort than burning files onto discs.