My best guess is the music would be supported by an SD card slot, and it would only support major formats like mp3 and wav. Nintendo's all about producing things at a low budget to target the largest audience possible, so throwing in a few unnecessary basic components which are already largely available on other portable devices, given they'll probably use cameras with low resolution and such to lower the cost, could result in a lower quality product all around.
They advertise that said features might be able to be used in games, but honestly, how many games could effectively implement such features, and how many of said games would be produced, given they wouldn't want to shut out current DS owners to avoid losing game sales?
If they offered a DS with larger screens, more internet security compatibility, and maybe tweak the elevation of a couple buttons, it would be a more worthwhile upgrade, and it wouldn't cost Nintendo all that much more to produce, anyhow. Or, if they REALLY want to sell me on a new DS, how about built-in TV output functionality, eh? It's already been done unofficially, after all, and I, for one, would be willing to pay a higher price tag for it.
As for music on the DS, in the off chance you're not using something else, there's already third-party options for the DS as it is. Why bother to build it into the system?
