Would this really be so complicated to provide such an aliasing feature?
Yes.
I'm not sure it would be
too complicated, but it's certainly more complicated than you've implied. First, I think we can agree an "alias" would at least serve as sort of a "shortcut" or link to a physical file in a different location, while otherwise behaving (as a library item) like any other file. That would be a nice solution for the issue I commented on—ensuring the collection only contains the best quality version of an otherwise identical track. But you want it to assume the tag values of the source track as well. That's quite a different matter. Not all the tags can be the same. Obviously
Album is different. Other than that, it may be safe to assume all the other fields should be the same, but how do you know for sure? Perhaps others should be different as well, based on the context of the album (or whatever the reason for the duplicate). Even if the developers could get away with arbitrarily deciding how that should work, what about custom fields?
Assuming there were a way to automatically clone tags from the original to the duplicate, then what? Should changes to any of the linked records result in the the change being replicated to all linked records? I'm afraid in some cases that's going to be undesirable. For example, the relationship of one duplicate to the original may not be the same as a second duplicate, yet changes to any one would affect all three. Assuming an alias is going to be "transparent" once created, this situation might even be dangerous—if the user is unaware of having created the undesirable result. No, I don't think it would be practical to link tag values. It would be handy to be able to copy or clone tag values from one record to another. Such a feature would be very useful generally, and should not be tied to duplicates (i.e., it might be convenient to clone a
similar record, and then edit it).
Tagging a file means always searching for duplicates first, then applying the tags to all the files.
Since I
never do this, "always" seems a bit of an overstatement. It may be a sensible approach if adding a multi-artist compilation album that likely contains duplicates. When tagging a single-artist album, however, I'm going to tag the whole album before giving any thought to duplicates. I might
then display duplicates and reconcile the minor differences that sometimes occur in track names. As for lyrics, I prefer to do them hundreds at a time—rather than by album—so I'm spending only seconds per track. Getting the lyrics from an existing duplicate—even if it's done automatically—is not going to make much difference.
Playing or burning or exporting or copying an alias file then means include 1 further step - to point to the "master file" and then perform the action.
These "master files" would need special treatment in other respects. Deletion should probably be impossible—until the links are removed. In some cases, copying an alias or a master is going to require clarification as to whether a copy or another alias should be created. And I certainly hope I'd be offered a way to replace a master with a better quality version—without having to jump through even more hoops because of the aliases.