Since it is a streaming box with a decent CPU, I think we are more likely to see a few software upgrades before any hardware upgrades. In general people don't upgrade their TVs and DVD/Blu-Ray players as often as their computing products therefore they will not want to upgrade their AppleTV every year.
All upgrades will be via added features and services for the next year or two.
Maybe games via iPhone and iPad?
The hardware can play 1080p video, but apple doesn't allow it yet, bc they don't sell/rent it and the files are huge, requiring users to have much faster Internet. Also in the USA, all/most cable providers only use 720p or 1080i video = current AppleTV specs
Most people sit far enough away from their HDTV that they can't even tell the difference between 720p and 1080p
Also 1080p will require new contracts with Hollywood
So given the capabilities of the current device and complications of making it better, I doubt we will see a new AppleTV 3 in 2011.
It will be cheaper for them to put A5 chips in a 2012 AppleTV 3.