I do believe that Titanfall will outsell Killzone.
The main core users of the Xone are there for the 'online experience', unlike the PS4. That people bought it for the 'diversity of genres' alot of people will skip KZ.
So, even the Xbone lacks on users, the users that are into FPS's and playing the shit out of them online, are majority on the Xbone. And I can see the gameplay is pretty much dumbed down, that's what the masses want, instant gratification, and have fun with it.
Come on, Titanfall is being labeled of the Xone savior! If it lacks on sales, that will be a huge disappointment and a big letdown.
That, and EA does a great job hyping games.