I think it would be nice if as a default device configuration the following is set to on, or a furios settings toggle is added in the UI:
AutoEnable=true
In the following file.
sudo nano /etc/bluetooth/main.conf
The user would then additionally set desired devices as trusted:
bluetoothctl trust mac_address1 bluetoothctl trust mac_address2
Then re-pair the trusted device
bluetoothctl remove mac_address bluetoothctl connect mac_address
That way with bluetooth on for example when you get into your car and it will connect to the car's bluetooth system automatically. When you exit the car and get back in after getting gas it will re-connect and allow you to play music without having to struggle getting it re-connected. Otherwise it take me about 5 attempts to reconnect, and it eventually will, but is not very efficient.
Ideally the part of having to know the devices mac_address should be managed in the gnome bluetooth settings itself (since it already knows the connected mac_address), which would simplify the second part of getting autoconnect to work.
There is one gnome-settings user story already (GNOME/gnome-control-center#2039)
