Hi,
I couldn't add some new suggestions at trello so I suggest something at this thread: Image Independence from sprite collection.
When I change my images from collection to collection, I have to change my animations also. If images are not depend on a collection then, it would be very flexible.
I change images from collection to collection, because I must arrange atlas usages, draw call count etc. if you make image (used in 1 animation frame) independent from collection then you can make atlasing dynamically and optimizing programmatically! I mean better fill rate, minimum atlas count, animation independence from sprite collection.
Another suggestion may be atlassing independence from sprite collection. This time, animations won't be effected again because of changes for atlas wastage or draw call count optimization..