That works when you are in 'gun range' of their cover and can shoot at them. But if you're pinned down? What about the enemies rear area where they are staging? How quickly can you set up and tear down a mortar emplacement?
Giving the soldier on the ground the ability to send a round exactly where they want to, behind cover, even inside a building. And I think you've created a very strong force multiplier. Given the the current state of the art in having locally operated visual recognition on the drone itself (http://www.csail.mit.edu/drone_flies_through_forest_at_30_mp...) to either avoid obstacles or target specific objects makes the weapon even more effective.
In my opinion when these things make their debut they will be as disruptive as the machine gun.
Now, maybe it would make more sense for the assassination of carefully guarded targets. But it will probably be a few more years before that technology is more reliable than strapping a vest containing c4 on someone.