Can't see it
From what I've seen, there are 4 main groups of music buyers these days:
1. people who buy mp3s. They already have an ipod or whatever, and this would be a step backwards for them.
2. people who download mp3s illegally. They also have an mp3 player, and wouldn't pay for this.
3. people who buy CDs because they realise that buying mp3s is bad value, so they get the CD and rip it. See 1 & 2.
4. people who still buy CDs because they don't get on with mp3s. This is sandisk's real market, and it tends to be people who don't bother with the latest technology and would rather stick with the ease of use of a CD. I just can't see them going for something like this.. they won't understand it, and it won't play on their home stereo.
Besides.. microSD? I bet people will spend as much on replacing lost cards as buying new music!