One of the reason DVD sales outperform CD sales is because with DVD's you get a whole disc of extra features - why couldn't that work with CD's?
I was listening to Off the Wall earlier, and after the last song Quincy Jones gives a few anecodtes about the recording process, talks about the different techniques used to achieve its sound, and there are also clips of home-demos of the songs - it puts the music into context and its all the better for it.
sure its a bit niche for some casual listeners, but then so are DVD featurettes about make-up and the editing process.
With any LP I like i'd absolutely love to hear interviews with the producer, outtakes, early demos, how they got the sound etc. If that process was made part of the album I'd be more likely to buy it for sure. Imagine Nigel godreich talking you through Kid A or something. Fascinating