GPS tracking was struck down on extremely narrow technical grounds - without a warrant the police do not have the right to trespass upon your vehicle (attach a GPS tracker). They deliberately did not rule upon the rightness or wrongness of tracking someone's public travel without a warrant. Since there will be no physical trespass when airborne drones are tracking our cars, that Supreme Court ruling isn't really relevant.

In my opinion, tracking someone automatically (either via GPS or drone), as opposed to having an actual person follow them, is sufficiently different in terms of cost that it becomes a qualitatively different phenomenon.