Apple TV Second Generation Not Supported by iOS 8
Developers of the Apple ecosystem today can get the second build of both iOS 8 beta and OS X Yosemite beta. Beta releases are usually for developing and testing purposes only. Developers use them to build and adapt their applications before the actual software release allowing them to release their updates and new applications as soon as the actual distributed version gets released. These beta builds are definitely for the consumer use. Beta builds of operating systems and applications is also a good indication of hardware supports; as in which hardware it will and will not support.
Now, Apple TV; the User Interface (UI) that comes with it is basically just another iOS for the larger screen. The iOS that is in the Apple TV supports its corresponding processing chip as well. The build of the iOS 8 would neglect some of the older iPhones inevitably due to age and the capabilities of the hardware itself, specifically iOS 8 will stop supporting the iPhone 4 running on the A4 chips. The second generation of the Apple TVs run on that exact same chip; the Apple A4. which means that the second generation Apple TV will not be getting new support or any more updates from Apple. To those who bought a third generation one though, fret not upgrade is still scheduled for your Apple TV as the iOS 8 will still support the A5 chip.