Asymmetrical Mob Texture Files

Currently there is no way to make say, a zombies arms or legs asymmetrical with a resource pack. I think that, for example, the zombie texture, should use the same format as the normal user skin texture. Same with the drowned, I noticed that the overlay for the drowned is a separate file. Just make all mobs that use the same models as a player use the same skin/texture format. And for the mobs that don't, just make the textures be different for each leg/arm. I just want the ability to make mob textures completely asymmetrical. As far as I know there is no way to do this in-game, but if there is, please let me know.

Edit: Also it would be nice if elytra could be made asymmetrical, too! :D