Google today introduced at Google I/O an impressive new feature coming to Chromecast in the future, where you'll be able to cast content without having to worry about being on the same WiFi network. It's all done through the cloud but allows you all the same functionality as if you were connected over WiFi.
The new technology can authenticate the users via the cellular connection to the cloud, or there'll be the possibility to use a PIN should this not be possible. This will be available to all Chromecast users and app developers later this year and looks to make using Chromecast a more social experience.