Hi Mitch,
To describe the feature I want to request, you might better watch the following vid.
I wasn't sure, if it's allowed to post a linkin a forum to a video of another software, so I do it right this way.
In this video from 56:45 ->
https://www.youtube.com/watch?v=lgJzZV1nty8
I tested the feature in anime studio. After implement such a function
you could easy mix various facial expressions in animation mode in spine.
It seems the actual skeleton reacts, how far/near the control bones are next to each other.
I had to move the set up bone to the left, move both eyes to the left also and repeat the same for the right direction. After that, the control bone could moved like in the video and interpolated the eyes movement.
I hope I described everything understandable, since my motherlanguage isn't english.
And later in unity, the control bones could also be used for realtime expression change and mixing^^
