Some bits to get started:

https://hub.docker.com/r/appimagecrafters/appimage-builder

https://github.com/AppImageCrafters/appimage-builder/blob/master/examples/kcalc/AppImageBuilder.yml

https://www.opencode.net/azubieta/podbird-appimage

kdenlive also has a good appimage

Craft is also able to create AppImage, probably the best since it allows to put all the dependencies requirements in one place.

Yes, the binary factory already outputs them, for sure on should aim to improve that method.

https://binary-factory.kde.org/job/Kate_Release_appimage/

ping @vpinon