low payloads seem to be addressed by those using drones already. I'm surprised at how much some of the little drones can carry.

Re. "spills", I doubt that drones will ever be as much of a concern as most ground rigs, regardless of the concentration. Seems that every year in NE IL, USA, there are bulk tender trucks and/or sprayers that get in accidents and spill. If you're ever in a tender truck or sprayer & dump over next to a river, you just as well start looking for your hari-kari sword. Life will be much better by using that vs facing the music. It's terrible now just getting hit & dumping diesel fuel.....or JetA anywhere near water. Relatively low amounts of high concentrates are easier to contain than high gallonages of whatever concentration.