They are already out there:
http://www.macobserver.com/article/2002/07/22.10.shtml
http://p2pnet.net/story/4203
None of them work with iTunes (which is a huge part of the iPods success) and none of them innovate or push, they wait for apple to make a move and then follow.. This will hurt apple if they stop moving but they have not yet done that.
Man, those are ugly. Worse than ugly, they look like knock offs.