I've got the Ivy plugin most of the way there, I think. It creates project libraries and applies them to the correct modules based on the Ivy configuration (thanks very much Christian for the example code!). It needs some touchups to the UI and definitely some work around managing the libraries. The biggest initial hurdle is that the library jar references end up being of the form:
whereas the ones created via the settings are of the form:
so the ones the ivy plugin creates are not actually adding to the classpath for some reason. I'm not sure why this is, as the method to register the classes just takes a VirtualFile, and the VirtualFileManager doesn't seem to like trying to create a VirtualFile with a jar:// prefix, and the VirtualFile I'm passing it is a valid file (jarVirtualFile.isValid() is true).
Anyway, I haven't had a lot of time to play with this over the last couple of weeks, and I'm probably not going to have a lot more time soon, so does someone else want to finish this up? Email me at email@example.com and I can send it to you... Maybe if more than one person is interested then someone can set up a version control repo...