Would it not be better to wait for the game to release before people get all upset. 900P with a good AA/AF probably would look just as good if not better than 1080P with medium AA/AF. The Developer might actually save some extra power for more effects and solid framerates that do not dip no matter how many AI characters on screen.
I really cannot be bothered about 900P vs 1080P as long as the game looks good, plays solid and is fun.