There wouldn't be any apps.
When they do this, they will do it like they did with part of the iPad... secret seeding to top devs they want to have in the store at launch. Right now iOS devs are all still recovering from having to crank out their iPad apps in a short amount of time. Personally I am thankful they have given us a break!
What kind of apps can Apple tout (and we write) when the remote is the only input device?
People said they didn't want another computer, so forget wireless keyboards and mice. Maybe a touch interface with the iPad mirroring the TV? You touch the iPad and the results display on both the iPad and the TV, but that would require you to own another device just to use it to its fullest potential.
When these problems can be reasonably solved, we'll probably have an app store for the TV.
I don't think making AppleTV owners also own an iPhone or iPad to get the full potential from the device is anything Apple would consider a negative.