Well, it sort of existed, then didn't. On Discogs, you used to be able to go to an album - say, "Assault Attack" - and you'd have all the songs. You could click on "Dancer" and get a list of all the different releases with "Dancer" on it. Now, this doesn't sound like much, but if you're a collector, and you're looking for that version with Gary Barden singing, and not Graham Bonnett hyperventilating, you could narrow down your choices pretty quick and find THAT version.
It was in "Beta" and they stopped it. Now, I have to search every release that MIGHT have it, to see if it's there, THEN check if it's THAT version.
I'd also like it if my DMV could have a database compiled of all the cars I've ever registered; make, model, VIN. I owned a couple cool BMWs back in the day and I'm looking for exact specs, and just can't find any of my records.