You can do this manually in Spine by pasting the right attachments turned visible at the right time, or try to automate this at runtime as you were suggesting. It would be a really cool script! 😃
I like the idea, reminds me of the custom script someone made for toonboom harmony that does a similar behavior by activating a certain set of images from an animation depending on the position of a bone.
I also have no idea of how this could work, and it is not possible to add such scripts specifically in the Spine editor only at the moment.
