Ron, based on shooting statistics, I wish that the police would exercise similar caution when they shoot. (Please note, that is NOT political or directed at any particular events. It IS however, a specific consideration discussed in the mandatory training in Kentucky to qualify for a concealed carry permit.)
Anyway, I believe that with good legal counsel he can make a good argument that it was not negligent, careless, or reckless based on that he hit what he aimed at and no other damage or injuries are being claimed. I already said that there could be a good argument for "reasonable and necessary," which is a valid defense against prohibitions on discharging a firearm in city limits.
Dropping charges against Meredith would do more to keep UAV operators under control than any revision to the Federal Aviation Regulations.