If it came out now, by the time Gears 3 and Uncharted 3 are out, no one will give a shit about Binary Domain's unfinished demo.
Now if they wait until February or March, most people who play those two games a lot will already be uninterested in their single player campaigns and will mostly only care for the multiplayer. As far as I am aware, Binary Domain has no competitive online? If it is long enough, it might get people really excited after they are out of Gears and Uncharted.