Yes, yes, and yes again! No one's figgered out how to stuff them thar
booklets into an iPod yet!
The last attempt at "bonus" materials on a CD was the CD-Plus format,
which was mostly abandoned because it stymied some older CD players,
usually involved automatically-triggered downloads of junkware if
inserted into a computer, and the "bonus" material was generally vapid
promo info and a jumpy low-rez video or two. Yuk! Most groups got
enough pushback from fans to just establish websites for this stuff.
Now, on the other hand, what would be truly interesting would be, for
instance, a running libretto for an opera, or a clever animation of a
ballet. Or, for a classic rock album, perhaps running guitar
tabliture. All of this requires skilled labor manhours to encode and
thus costs money and thus will not be forthcoming from Big Music.