This is kinda like my idea of adding "Specify Bitrate" to the output quality of the files to be burned to disc rather than just the options of High, Medium, and Low quality.
I like your idea too. It would be nice if they added a feature to automatically fit to disc regardless of how many video clips you have in your project, lowering the quality of the video(s) to be burned to fit the disc and then reporting on how the quality will be after auto-fitting the files to disc such as (Great, Good, Fair, or Poor quality) something to that effect. Nice idea.