Screen spluit helps that great , do You plan to add an option so when you open big image then canvas size is resized to fit it in? When i open big images then i have to scale up canvas size myself , it would be convenient to detect the size of first imported image and set canvas size to that.
And they shortcuts for next/previous keyframe is the thing i personally use a lot, saves tons of time, i dont have to hunt for exact keyframe with mouse cursor.
Ah also, transparent colour( first one in palette) it would be nice if we could set it to display transparency, so if we have portrait image and background behind character is pink colour, and this colour is first in out palette then it would not show up in preview cause its transparent , but this would be nice as optionable not default .