The operating system is said to be more 'feature-complete' than the one currently running on the device and is apparently the one that Apple's rumored television will run.
We've heard Apple is actively trying to court manufacturers to use a new "control out" API in order for third-party manufacturers to make accessories that are compatible with the new Apple TV OS and the upcoming "iTV." It's said that by using the API, it will be possible to control any connected components all from the Apple remote (and the Apple remote iOS app as well, we're assuming).
The 'control out' API is said to even allow control over the guide on cable set top boxes.
Apple has announced that the WWDC keynote will take place on June 11th at 10:00am PST.