What you are saying is true, however it is a rather messy solution. Assuming that the next AppleTV will support 1080p output you could not just mirror your screen to get the best quality. The source film is in 1080p, gets scaled down to screen res. which is transmitted to the AppleTV and then gets scaled up to 1080p again - resulting in a easily visible quality loss.
I hope they treat the screen as a "second screen" which is mirrored...
I hope they treat the screen as a "second screen" which is mirrored...