Driving mode
Having a toggle (plus perhaps integration into say puremaps so that if directions are being used for car navigation it will automatically toggle the mode) for a driving mode in the shell or in spacebar (either way would require integration with the SMS system) would be a great feature for safety. While you can answer calls usually in a car using a headset or just quickly tapping answer, it is not safe nor legal to view or reply to a text as it takes your attention away from the road. Blocking text notifications while driving and sending a customized message to those who text you telling them that you are driving and will respond as soon as you arrive at your destination would prevent the driver from being distracted. For urgent messages it could detect a trigger word such as "urgent!" to let through messages from the sender.