Feature Request Using per animation avatar mask in animator layer

Hello!
I need for the game I am making an animator layer for different character reactions that may use one hand (waving, raising the hand, grabbing things), two hands (applause, cheer) or the whole upper body, to play on top of the movement layer (idle, walk, run).

Similar question was asked before (https://forum.unity.com/threads/per-animation-avatar-mask.1511645/) with no official response.

As the documentation states, you can select an AvatarMask when importing Animation clips, that will discard any other animation. I thought that putting those animations on an additional layer would only animate those parts, effectively acting as a mask. However, the masked body parts fall back to that "default avatar fetus pose".

The problem is, at the moment, the only way to add those animations is to create 3 layers, one for the spine/chest/head and one for each arm/hand, which feels overcomplicating the animator.

IMO, the animator should fall back to the upper layer when animation is missing for some body parts.