Reopened because of another idea that came up in Discord that's related to this - the option to explicitly specify random music.
I see three forms of this that could be of interest and that I'd be willing to do if the interest is there:
a) Allow overriding the "level 1 plays track 1, level 2 plays track 2" etc aspect of using music.nxmi, in favor of "each level picks randomly", as is what happens with loose / testplay mode levels currently. This would presumably be specified in the music.nxmi itself, so can be applied (or non-applied) to any scope which a music.nxmi itself can be.
b) Expand the explicit "play Xth music from standard rotation" specification to also have a "play random music from standard rotation" option.
c) Where a priority order is specified in music.nxmi or a level file, provide a way to specify that the priority order should be shuffled - thus, essentially, this is "specify a few choices, and pick one at random, ignoring those that don't exist and maintaining existing fallback behaviour if none exist".
In the case of C, I'm not willing to get into complex interactions. The randomness would be all-or-nothing. So you could tell a level "pick one of blah, derp, zonk, weep, orig_07 or orig_10 at random" (and it would ignore any of those that don't exist), but not "pick one of blah or derp, if neither exist pick one of zonk or weep, if neither exist pick one of orig_07 or orig_10".
And to be clear, these three are not mutually exclusive.
Is there enough interest in such a feature?
(EDITED 29/06 for clarity.)