I think Slingbox and SlingTelevision are two different things. I tryied to login with my slingbox account and I was unable to do it. I thing Sling will not release an AppleTV app for slingbox (slingplayer) because it is a "competing" product for their own "television" product. They want to sell their "television" service, not the "hardware" and the slingbox (slingplayer).
I am very disapointed and very upset with the way this company is doing business.
I am also hoping Sling's Apple TV app can be used to control my Slingbox. I am concerned that camiloorozco is right, though. I tried getting info from Sling TV via their online chat, but they could not tell me for sure if the Apple TV app works like the Mac app, in that it can connect to and control a Slingbox. I only have an old Apple TV so can't download and test the new Sling app, which only works on the current generation of Apple TV.