@AC: fail

I see your point. But the big problem with aiming a sodding great rifle is the sodding-great-ness of it, and hence the extreme skill required to shoot without any kind of tremble in your hands. Laser designators are the size of a camera, mount on a small tripod, and the better ones have all sorts of assists for getting the targetting right. AFAIK they don't currently have ones that can track a target as he walks, but it's almost certainly only a matter of time. So it's going to be easier to do with a separate designator.

Don't forget about the problem of showing yourself to fire, and if you're firing directly at the target then they can see your muzzle flash. With this beastie, you can stay behind cover, bash a round into the air roughly in the right direction, and your mate with the laser designator can steer it onto the target. Hell, your mate can even be behind cover too and use a detachable control panel to drive the designator.

And it's worth pointing out that this will tie in perfectly with the XM25 smart rifle, also a smooth-bore weapon. A smart fused payload on a smart targetting shell is likely to be rather useful - think grenade launcher with sniper-rifle accuracy.