Somewhat off topic, but I'd be really happy with an mp3 player for the Z that has some of the features of an iPod, even without access to the same content. Important features missing from the Z's mp3 players that I've tried (xmms, mediaplayer, mediaplayer2, and something else...) are:
A laudable aim, I agree, however some of the features you want are already present.
1. Random play
This is certainly supported by xmms - there's a little button on the gui you need to press.
2. Sort/Select/Play by categories (genre, artist, preferred, least played, most etc.)
This would be useful, however I wonder how much storage would be required for the database which records the most/least played info.
3. Saved playlists (ie, last played, high preference/low preference, genre, etc.)
stored on (or associated with) different media. For example, I store music on CF
cards, and it would be great if each card had it's own info, rather than just a single
playlist organized by song title (ie., directory listing)
Multiple playlists are possible afaik with all of the above, however you'd need to save them in the default location (under ~) and load whichever one was for the card you've put in.
4. The ability to lock the keys, so that the arrow keys don't change the volume/song
I just close the lid
5. Repeat (by playlist, not by individual song).
Again, this would be an interesting thing to have. Take a look at opie-mediaplayer2 and make some changes to it,