Man, I wonder if we'll ever see a release for this or Automata with all variations mixed into tracks in a way that shows them all off properly but without too much repetition. I might make some mixes myself like I sometimes do, but the opera boss in Automata in particular has sound effects timed to the music which I bet will be hard to get hold of and mix into tracks the same way the game does.
Edit: I made a couple of mix tracks from the files in this thread, ones that I know are missing from the OST release. Specifically, versions of Hills of Radiant Wind and The Lost Forest that transition between the percussion and calm versions, and a version of Shadowlord that transitions to music box solo at the end, like what happens at the end of the battle in the game. I'll post links in a few hours once my MEGA transfer quota isn't maxed.
I tried to do something like what you talking about with Drakengard 3 soundtrack. But I ended up with making 3 different versions of each battle track (additionally to the released soundtrack tracks) lol I know it may be stupid, but it is better to choose the best version you like from a few 4-6 minutes long tracks and listen to it whenever you like, then to make a long 10-15 minutes version, that contains all possible variations, in my opinion. You can check it here on my channel:
https://www.youtube.com/watch?v=cO6ssub4wJw&index=3&list=PLiVSF2AAhkqdazW6HrsOI56JV2SwWa-NG (there is no download link there now, but I will provide it later, didn't finish the whole thing yet)
Well, it is not Nier, obviously, but I guess I will make the same thing with both Nier soundtracks as well. Well, check it out, if your'e interested.