What we'd like to be able to provide:

• Single click installation
• Update check/Automatic updates
• Simple distribution to as many distributions as possible

Flatpak relies on distribution support to make some of these things happen. Single-click installation is atm. not available and updating is not yet widely supported by package management.

App image seems to be working on a solution that would allow Kube to self-update.
https://github.com/AppImage/AppImageUpdate/issues/30

On Windows/OSX the options are either the store which would handle distribution and update, or doing something self updating like browsers or telegram do.