You probably get those sugestions a lot, but I feel like they would improve the program immensly!
It would be amazing if we could get a layer interface just like the one in sketchbook, as an artist and animator I personally use a bunch of layers to keep my pictures clean and very easy adjustable and the limited amount of layers and the fact that I cant lock those is making it really hard for me to use flip book.
Another hting that bothers me is that the background layer always stays the same and cant be changed for each idividual frame.
And the probably mostasked feature for all animation programs: an audio track. it makes animating things like lip sync so much easier and is a feature that many animators find incredibly helpful!
I saw the suggestion of a dark design theme here and i couldnt agree more! The light theme makes it really hard to animate when its night time or just a coudly day. Its quite hard on the eyes and i personally get a headache from it easily.