We'll see if Unity's Timeline API will allow us to support this.
Currently, the SpineAnimationState Clip type only calls AnimationState methods. So Timeline itself doesn't handle applying the animations. We went this route is because different tracks on a timeline are sort of hidden from each other, which makes Spine mixing act unpredictably when there are multiple clips mixing, and when AnimationState is doing something itself.
It's also done this way so that even after your timeline playable ends, the animation can continue playing.
For now, you may have to get those target SkeletonAnimation components and also set their TimeScale
to 0 when you call PlayableDirector.Pause()
.