I’ve got a new project right now. What I want is a central repository for all media. From music to movies and pictures and ultimately PDFs. The Home Sharing feature of iTunes is close but the problem with it is that our iTunes libraries are on laptops and they are either not always powered on, or are not physically around and on the network. Also, i would love to merge multiple personal libraries into a single common library, but maybe not everything is worth pooling together.
I picture it as a SQL back end that different instances of iTunes can communicate with. Of course, what would make the whole thing work is that the Mac version of iTunes (and additionally iPhoto, etc) have scripting hooks built in for AppleScript manipulation/queries.