+1 for this. I think I ranted about a similar feature last year. XD
Similar use cases do pop up at the forums every now and then.
"Shake head" is a good example of an animation that needs this.
I'd love to show and hide groups of slots (and bones?) easily, for the purposes of having "head states", and "torso states" and "arm states" and "leg states", different states which are easier to manage if they were comprised of a totally different set of slots. (and bones and bone setup poses, I guess)
I think UbiArt games use this technique a lot. Their characters certainly do a fair amount of state changes for heads, bodies, limbs within animation clips.
On a related note, a feature like this could also solve many problems for multi-directional animations for top-down or isometric games.
A character could be allowed to do a spinning animation, or some other animation that involves turning. And separate skeletons for each direction won't need to be managed at runtime, since we can assume that not only could individual parts be turned on and off, but entire bodies.
No rushing Nate though. He's doing good work!
This is uniquely a 2D skeletal animation problem that needs to be solved. And given how Spine is set up, a good solution for this isn't very obvious.... not to me anyway. >_>
