Possible additions to improve system integration with the AppImage spec

Exactly, nothing should need to be configured. It needs to work out of the box.

As for the executable bit, please see

Ideally desktop environments (Gnome, KDE, Xfce,…) would ask the user whether a file should be made executable when an ELF (application) file is double-clicked that is lacking the executable bit.

Please request this feature from your desktop environment of choice in case it is not available there yet.