Additional content channels are slowly but surely appearing on the Apple TV. As others have pointed out these channels are likely being developed by the content providers themselves. This 'invitation only' SDK for content providers is a logical step, a move toward the creation of an ecosystem but short of a full public SDK that at this point seems premature.
The popularity of the Apple TV increased dramatically as the device metamorphosized from a 299 device with on board storage to a 99 streaming box. I expect the 99 price point to remain, along with the inherent processor and storage limitations, and basic interface paradigms.
For the near future, I think the Apple TV will remain effectively as-is. Any open SDK would surely encompass gaming, and any dual screen (iPhone and TV) or gesture recognition solution seems inelegant and unlikely. I can see the case for a whole-hog iTV, a dramatically simplified no-box solution with integral FaceTime, killer audio, and big screen gaming. But for now, I think the current Apple TV will remain and it's development will follow along the current trajectory.
But as the number of content channels expands the existing remote interfaces feels increasingly tedious and limiting, the lack of a global search function increasingly glaring.
The fundamental interface question is focus - eyes on screen or eyes on remote. Via simple directional and hierarchical physical buttons, the click remote allows user focus to remain entirely on screen, a quintessential element of at least the traditional the living room experience. But the current iOS remote interface seems an opportunity squandered—easy keyboard access a poor trade-off for the elimination of orienting physical controls, occasionally requiring a glance down to a nearly blank device screen in hand.
There has been speculation of a new class of touchscreen remote, something the size of an iPod Nano. I don't see the case for this. This would suggest some type of on remote interface, but given the limited screen size this would surely be a tedious experience. Concerns of cost and convenience seem to eliminate any remaining appeal (does anyone want a dedicated single use device that they need to charge regularly?). The iPod Nano is a backward looking concession to a faded market. I don't see Apple introducing a new touchscreen device that offers a poorer experience than an iPhone or iPad. The interface is best on the big screen and/ or on the iOS device that you (most likely) already have.
The current paradigm of included click remote and expanded control via iOS app works, and ensures that the $99 price point can remain. But if is Apple is serious about voice recognition, Siri, in combination with global search would be a boon to content discovery and selection.
If technical limitations (primarily batter life, and to a lesser extent cost) can be overcome, voice control via a low power Bluetooth click remote would allow far more control without added complexity and allow focus to remain entirely on screen. Conversely, an enriched iOS app experience, something similar to the iTunes or App store interfaces and allowing similar fine grained levels of control, would allow expanded control via an on remote interface, the big screen remaining dedicated to content. Siri would also play a part here.
These two methods of control could coexist, expanding the baseline level of control while providing a new but familiar iOS interface, all while maintaining existing price points.