Hello I think it would be useful to have a brush mode that colors in the frame using either previous or next frames.Let me explain imagine you are animating and the arm is in the previous position but not the leg os in stead of redrawing the arm you just invoke this brush mode and it repeats the frame section for you. if you have any questions I will be glad to clarify.
I need some more explanation on this please 
You want to automatically copy some portion from the previous frame to the current?
The portion is selected in the current frame?
Hello Jan@cosmigo think of it as a clone tool that clones the frame ahead or the frame behind depending the mode that is selected.Take your typical frame you have elements that will be repeated in the frames and you have frames that will not.
This tool allows you to instead of reinventing the wheel and copying and pasteing and lining up the animation so it won’t stutter when played this tool allows you to copy some parts as long as the animation is in the same position.
In this example you see the body and boots are in the same position so when using this mode you can redraw the frame.Once the whole frame is copied you can add extra elements that don’t exist in other frames,
Lastly it would be cool if when you had the animatiion timeline selected it would get cloning info from that frame instead of the frame ahead in fact it might be nice to have in the tool and paint settings : before frame /after frame/ selected frame/ key frame…