Add Event to modify the list of javascript files before they are processed. This allows plugins to not have their - or other plugins - script delivered to the client. Creating the list of files upfront might add a little overhead which I think is OK when you can be certain that only JavaScript that really is needed will be delivered to the client.

Multiple Javascript requests, e.g. to only send the jQuery part or just editor/administrator scripts, could be implemented with this modification (I know, jQuery has already been split).