It's interesting because it implies that music is finite. Or possibly that commercial music is finite - there's an infinitely long tail of weird shit that we don't want to listen to, but the stuff we do want to listen to is confined to a finite segment of possible music.
If so then eventually all music will be free, because it will be repeating a previous iteration of the same tune.
This also implies that music is discovered, not invented.
Do you mention the distinction between creation and discovery because it's a distinction in law? Cos it seems intuitively obvious to me that distinguishing between creation and discovery has no philosophical merit - creativity happens within many finite domains, the size of the problem domain really has little relevance to something's artistic value.
The exhausting of useful chords as you describe has both already happened and will never happen. There are countless songs already based on the most common chord progressions, but new ones will also continue to be found for the foreseeable future. We're nowhere near knowing the size of this domain.
If so then eventually all music will be free, because it will be repeating a previous iteration of the same tune.
This also implies that music is discovered, not invented.