With no content storage and 100% streaming, there's no reason this couldn't work from any iDevice to any AppleTV. What I mean is: Say you have the MLB app on your iPhone, but your friend doesn't but he has an AppleTV and giant screen. You go over there with your iPhone, tap a single button, and you can both enjoy the game on the big screen. There's no syncing or sharing of iTunes accounts necessary. The same for sharing and enjoying movies and TV shows with friends. This is exactly the element that's missing in almost all current online content delivery schemes.
MLB At Bat just added video out via the iPad VGA adapter just a few days ago so they're clearly comfortable with the concept of using the iPad to stream to a TV.
With no content storage and 100% streaming, there's no reason this couldn't work from any iDevice to any AppleTV. What I mean is: Say you have the MLB app on your iPhone, but your friend doesn't but he has an AppleTV and giant screen. You go over there with your iPhone, tap a single button, and you can both enjoy the game on the big screen. There's no syncing or sharing of iTunes accounts necessary. The same for sharing and enjoying movies and TV shows with friends. This is exactly the element that's missing in almost all current online content delivery schemes.