This is absolutely low-priority, and you are not supposed to take this request too seriously. Anyway...

As the title already says, I would love more boss music from the game. Why? Because almost every single piece of music in this game is fully loaded with epicness, that's why... well, okay, not only.
In fact, while the current theme sure is pretty damn good and I don't even want it to be removed completely, it sometimes doesn't blend too well with the boss itself. Sure, organ-music and stuff is pretty damn nice, and I would be lying if I'd say that I don't like it. However, I just think that custom pieces for different bosses(besides danger missions) could accompany the boss even more, for example hinting at its difficulty(isn't it awkward how Snarby gets the same dramatic organs as Dark Vanaduke?) and using the instruments from the previous levels to make the music blend with the whole boss stratum.

So yeah, what would be some possiblitys?

General stuff
As the current boss themes already seemed to introduce it like this, all boss themes should be more or less be variations of the current one. Instruments, pace and overall track can be changed, but the new boss themes should preferably resemble the first one in melody.

Based on the stratum
That one would require more soundtracks than the other option, but it would enable using the respective instruments of the boss stratum to make the boss-fight blend in and thus give the fight a better atmosphere. For instance, how about giving the Roarmulus twins something slow, menacing, with the clunks and machiney feeling of the actual stratum music instead of the organ and steel drums? It would underline the atmosphere of the place and the fact that you are basically fighting against what's supposed to be war machines. Or give the slime king a theme that resembles the whole places overall goofyness(like the actual palace-music)?

Seperating between shadow lair and normal clockworks
Simple enough: Give shadow-lair versions of the bosses more menacing and dangerous-sounding boss music. Preferably a straight remix of the current theme with some extra stuff added, because that's also the description for the shadow lairs, after all(fighting harder versions of previous boss strata).

Tier-specific
Similar to the shadow-lair one(both can be combined, by the way), this one basically keeps the old boss music, but adds a bit more to it with every stratum.

So yeah. As I said, adding some more boss music that actually reflects the bosses you fight in any way is not mandatory, but a very neat little feature that would give the boss battles some more character.