Oh dayum, sweet! Works like a charm :D Although I got two points of feedback here:
1) When I move my selection and some pixels leave the canvas, they are erased. This is not a desirable behaviour for me as I sometimes do this to see if something fits, and sometimes I may move my selection again but I can't right now as this erases pixels.
2) I recommend either creating a button or some documentation about this feature, I mean, you cannot expect anyone to read this comment, right? :p
Ah and another thing, I really like the fact that a flatpak and such exist. But a lot of the Linux desktop users still use .deb packages. And with good reasons too. That is why I just dropped the zip somewhere on my hard drive and use a terminal to open it. But installing this using "sudo dpkg -i Pixelorama" or "sudo apt-get install pixelorama -y" would be a hell lot better. If it creates a launcher too it would be perfect.