I really love this idea. Take as an example the UK and US versions of "The Clash" (first album). They share 10 songs in common out of 14 and 15, respectively. Right now, is see two approaches: 1) rip both albums in their entirety, doubling the necessary disc space for the ten, or 2) rip one album with shared tracks in its entirety, only the non-duplicated tracks for the other, and then create a playlist re-building the entire other album. But I think most MC users conceive of playlists and albums very differently -- we want actual albums to show under Artists/Alblums in the Audio tree, whereas playlists are for dance mixes, collections for moods or BPM or whatever, ways to organize transfers to external devices, etc.
So to expound on hit_ny's original idea -- Perhaps the ability to drag & drop a track from album A to album B, where it would do something like pop up a dialog box asking for track # and any other relevant information, but otherwise would take on the attributes of what it was being copied to. And most importantly, you would not actually be copying the song, just providing an alternate set of tagging information (?) to avoid using the extra disc space, or the confusion of creating a playlist where you really want to see the tracks in album list style.
(Things would of course be a little more complicated if you selected such a shortcut, or placeholder, or whatever you'd like to call it to transfer to a portable device, or to burn a CD. Should it copy the linked-to file? Probably...)
Thanks!