Improved Multiplayer mode, with more game modes, some vehicles, and more races (I would love to see a 'swarm' mode similar to Dead Space 2, with the Tyranids on board a Space Hulk.)
As for the outcome of Titus, either he would become a member of the Deathwatch to investigate rumors of the Necron Threat at the edge of the Galaxy, or his connection to the Warp leads him into the arms of the Grey Knights.
Also, Just to get the fanboys into a froth, toss in Cypher and have his chapters getting progressively closer to Terra, with the last chapter at the foot of the Golden Throne itself.
Also, I happen to like the Game Balance. And I don't know about some of the people, but the Bolter is a darned fine weapon even without the Kraken or the Targeter added on, and once those are on it becomes a boss.
Me, I use a Storm Bolter + Melta with rapid deployment, so I can basically pop onto a contested point, usually score one or two kills and keep the other side from capture. Either that or I sneak over to their closest control point while they're fighting the middle ground and take it. Such fun.