I think I've suggested an idea somewhere where many performances of the same song appear on one release, but a new idea I've had would be a DVD of the songs that have had the most performances... And combine the various renditions in one montage. Like the "C is for Cookie mash-up" that appears in C is for Cookie Monster.
It could have mash-ups of the various versions of Rubber Duckie, C is for Cookie, I Love Trash, ABC-DEF-GHI, Sing, and What's the Name of That Song? In fact there could be a super-long mash-up of The People in Your Neighborhood, showcasing a lot of different people in the neighborhood over the years (i'd say the same for One of These Things, considering all the versions there were during the early years, except that song is kind of short for a big mash-up).