>But against small units of well dug in, or hidden enemies - mortars, snipers or troops in trenches, I'm sure they'd be great. I'm thinking basically a grenade with wings that can hover, spot a target and be guided by an operator ~1km away.

I don't know why people insist on flying grenades with lots of electronics. That is very expensive. It would be more logical to use the drones for physical target acquisition and surveillance and then use an actual grenade launcher or other conventional weapons to do the killing blow.