Raytheon Eyes Sidewinder-X Upgrades

It appears to be a significant improvement on the original AIM-9X, with lock on after launch, and could drive the move to a new rocket motor, the rocket motor on the AIM-9X is the same as previous models, as it would allow launches to longer range.

From all I know about the missile, the kinematics (basically range and long range maneuverability) are not that good, having a single pulse motor (with thrust vectoring, you want lower thrust at the start in order to make the vectoring work better) and being smaller (5" body diameter as vs 6") than many of its competitors.