Very nice, i've been using piskel but this would be ideal to use with godot. I have a few ideas if you want to look into it.
* preview window of animation sprite that can be scaled up/down, and play independently of the frames at the bottom (playing automatically at 12fps when program is started)
* moving the frames closer to the canvas layer window
* have up to 4 texture buttons for the brush sizes, optional textedit for larger values
* compare with Piskel, have the +, -, and clone keys embedded in the frame you have active.
* move the loop/playforward to bottom, bringing the + - CL keys closer to frames
* a checkbox to show/hide the onionskin
* up to 4 texturebuttons for onionskin, with optional edit box if you need more onion flavor
* more defined border around the line of frames at the bottom.
* hotkeys for the button 'frames' +,-,CL, etc . playing with the source, I added Z to create a new frame, X to delete a frame, and C to clone it