You asked. You begged. You pleaded. And your requests have not fallen on deaf ears... but it did take HBO a while, didn't it? The HBO GO app got a small update this morning, adding support for Google's streaming Chromecast dongle. Nothing more, nothing less.
After today's update to both Google's Chromecast whitelist and the HBO GO app itself, there are still just four third-party streaming apps that are compatible, including Netflix, Pandora, and Hulu Plus.