As a standalone TV (with the current Apple TV built-in), I don't think it is much value if you still have to hassle with the cable/satellite DVR and all the other complexities associated with a normal entertainment center, such as a Blu-ray player, game console(s), and a receiver.
I think their end goal is something along the lines of all content, anywhere, anytime, on any iDevice, including the TV (and also Ipad, IPhone, IMac, etc.)
Assuming they could work out the content deals with all the providers, the main issue is bandwidth for an IPTV type service. With Cable or Satellite, I can have multiple HD streams in the home without impacting my internet service. Good luck trying to get 3-4 HD streams plus normal internet use with any current provider in the U.S. Even without the 250 or 300G limit montly cap, there just isn't the bandwidth available to do IPTV nationally (or even globally in most locations) in a way that can compare to Satellite/Cable TV.
Then, for integration with receivers, blue-ray players, game consoles, they really need to have some sort of simplified experience like what Crestron & AMX have, or better, something like Savant. Not sure how they could do that.
Otherwise, if all the 55 inch Apple TV does is remove the need for the current Apple TV box, and you still need a universal remote of some kind along with a receiver, blue-ray player, game console, cable/satellite DVR, I can't see how that would be such a revolutionary device that would make people want it.
Compared to the TV/Home Enterntainment area, the Iphone and Ipad is child's play, since there is just one device with minimal peripherals (other than say, headphones and a case). The TV/Home Entertainment area is so much more complex and that's while it's taken so long for them to figure this out. If they come out too soon, then it'll just be another boondoogle like the Google TV box.
But, if they can make some sort of TV that can truly replace all other components or integrate in some revolutionary way, then they could really have a winner on their hands.