As hinted at through the introduction of the iCloud-based Family Sharing feature, the latest beta of iOS for Apple TV (along with the corresponding Beta 2 of iOS 8) doesn’t support second-generation Apple TV units, which were the first model to sport the small-black-box look of the current (third) generation devices. The second-generation models can be distinguished from the later version by not having support for 1080p output, and by having an Apple A4 SoC — the same model that powers the iPhone 4, which is also no longer supported as of iOS 8.
It appears that the third-generation Apple TV will soon gain some of the new features touted for iOS 8, starting with the Family Sharing feature and apparently expanding to selected bits of “Continuity,” a technology included in iOS 8 and OS X 10.10 Yosemite that allows seamless resumption of activities from device to device. On an Apple TV, it could be applied by offering the user the option of instantly continuing a song or video from the exact point it was stopped on a mobile device or Mac.
Because the four-year-old iPhone 4 is no longer supported in the forthcoming update to iOS, it makes sense that an Apple TV sporting similar hardware specs would also be deemed not compatible. While owners of the second-generation Apple TV (which originally debuted in September of 2010) will miss out on new features included in the iOS update for third-generation devices.
