The new toggle hints the release of “iOS in the Car” which was first mentioned at WWDC 2013. iOS in the Car allow users to attach their iPhone 5 or later to a supported car’s console which then provides an iOS-like interface on the car’s display. From there, you can access Siri, maps, music controls, send and receive text messages, and make phone calls hands-free. According to Apple, it will seamlessly integrate iOS to your car’s in-dash system.
The toggle for Car Display can be found in the “Restrictions” tab in the new beta. Right now, it looks like Apple is planning to roll out the feature with the public release of iOS 7.1.
Along with the new beta, the 120 MB update offers other minor changes. The “dark keyboard” option from the first beta has been removed. The Touch ID and Passcode settings tab have been moved for easier accessibility. It can be found between Sounds and Privacy instead of being buried in General. An all new option that allows users to turn on button shapes can be found in the Accessibility tab. This feature creates a darkened shape around navigation buttons (such as General, Done, etc.) which help users identify the difference between a button and the heading.
Source - Apple