I believe you can patch in the original CD music and it's not that hard. It is however, somewhat questionable legally speaking, even though Trent Reznor doesn't seem to care one way or the other.
And yeah, this is a textbook example of the kind of thing that should have involved a lifetime license. I thought the music was written specifically for the game and hasn't been released independently of the game.
Those are all well and good until Uuhd/16K games/media come out and we all need xetabyte(spelling?) drives.
I'd personally rather have higher quality AA and lighting effects than arbitrarily large numbers of pixels at this point.
That and a game where things sitting on tables randomly start levitating because I bumped into the table.
Imo if one had a copy in the past and it broke/got damaged and they bought the GOG version to replace it then they should be legally allowed to.....and for all others to me it's only fair, irregardless of what Trent/etc says(depending on if he had it removed or the music label did).
Also it's similar to the whole deal with some games(racing iirc) having a limited window to use certain makes/models in their games for only a set period...I could be wrong though.
TO be fair, I think we only need even those kinds of improvements to a point...eventually the barrier past which our eyes/brains can't tell the difference will be reached/crossed and/or stuff will reach into uncanny valley levels of realism only suited for VR.