Something I've been wondering about for a long time, which has applications here, is the idea of being able to split up sprites into regions or areas. It'd be useful for, for instance, fighting game collision detection (ie. did the enemy collide with a fist or just the body* or where did a specific punch land), or switching out segments of a character (like how the old LEC games worked, they didn't store the whole sprites each time, just the segment that was changing) or for having characters only being partially tinted by a region (for instance, so you could have them standing half in shadow, half in light)
*A nice and simple way to achieve this with existing behaviour would be to check if the sprites are colliding, then also check if the current frame of the player's (or enemy's) view. This would mean that the player would have to "punch" to cause damage, not just collide by walking into the enemy.