The similar idea I've been pondering for a few years now is a drone with a laser-scalpel of some sort, paired with a ring shaped net to prevent the coconuts from splitting when they hit the ground. The laser would cut the whole cluster, instead of individual coconuts, for power-consumption's sake, so the net would have to be strong enough to accommodate that. I pondered it with a saw blade at first, but the cluster's stem is not firm enough, making it hard to even saw by hand with a pole saw.