This is a feature I've asked for as well. The ability to customize what columns are being shown in a miniskin playlist as well as their widths... actually, I just had a better idea. Make the playlist object more robust in that the end user can resize columns, and access some sort of config screen that lets them choose which columns are being displayed. That would also help preserve the integrity of existing skins, as the authors wouldn't have to go back and change any of the code within their skins to specify which columns are being displayed, etc. Let the skinners just use the playlist object the way we are now, and leave the customization in the hands of the users.
On top of that, I'd like to see some more options for text displays, so that, for instance, the text could be centered if it fits, but if it's too long it will automatically scroll or something. And being able to control the speed of scrolling text would also be nice.