Add subtle battle themes for the remaining bosses

The Ender Dragon has a "boss theme" consisting of mostly static noise which barely anyone knows, but it allows pack creators to easily customize the song by replacing it via a resource pack. The other bosses lack such a feature and its a bit painful to add boss themes to them. Currently the only way is firing playsound commands via an every-tick-function, which is really hurting overall performance, breaks easily and is not good coding. Would it be possible to add generic, barely recognizable background music to the Wither, Warden and Elder Guardian Boss Fights? A simple track, barely noticable, maybe some screeching souls for the wither, water bubbles for the Elder Guardian and cave sounds for the warden. It would allow the community to easily make more immersive content featuring epic boss music.