Add "disable WiFi if wired" configuration
It would be extremely useful for desktop environments to offer users the ability to automatically disable Wi-Fi when plugging in a wired network. The main use case would be for power saving, as plugging in the LAN cable shows that the user presumably wants to use the wired network.
This could obviously be implemented in a user session helper, but it would require much more care to be done at this level, and would make it become a user preference which couldn't easily be applied to the whole system as it would be if implemented in NetworkManager.