The upcoming iOS 5 software has pretty clear indications of support for Bluetooth keyboards for the second generation Apple TV. 9to5Mac reports that several hints of keyboard support are embedded in the code for iOS 5. It would be a welcome update.
Using the little stick remote that comes with the Apple TV for entering text is like descending through the levels of hell in a Bosch painting. The Apple Remote app for iOS certainly helps, and allows you to use your iPhone or iPad keyboard to enter searches, but full keyboard support would be a great way to go, especially for Apple TV owners who don't have iOS devices.
The Apple TV hardware has a Bluetooth chip on the motherboard that has been silently waiting for activation. If the feature does appear, it could also open the door to other devices like game controllers if Apple allows iOS games and other apps on the Apple TV.