using duplicated groups for more parts that use the rotation values of vanilla parts is rather limited, because they cannot be parented to other parts and must remain in the root

animations can already take a math equation as an input, however this just turns the value in the box into the result once you click away and back

one should be able to input an equation that uses variables to use in such locations, for example say one wanted to have some long hair that would dangle off of their head without stabbing through their chest should they look straight up, they would go to add a global animation to the hair part and input something like "(-headRotation.x)" into it s X rotation, while leaving Y and Z alone, therefore the hair would then only rotates the opposite of the up and down rotations to stay pointed down

I can think of plenty more applications of this, extra arms or legs parented to the body with these put as their rotation values and therefore much easier to account for placing in the right spot in animations such as sneak and crawl, custom wings using the elytra rotation anims that are parented to the body, bits of dangly fabric here and there using the cape rotation to flow in the air as the player moves around