IDK...perhaps a time limit to implement for the patent to be registered?
You can hold a Design Patent for 2 years, after which if you haven't achieved a practical prototype, you lose patent rights.
Maybe something along the lines of a "Provisional Patent Application" (which lasts for 1 year)?
Drones are, in essence, flying autonomous vehicles. Pros and cons surrounding drones today might well foreshadow the debate over the development of self-driving cars. In the context of a strongly regulated aviation industry, "self-flying" drones pose a fresh challenge. How safe is it to fly drones in different environments? Should drones be required for visual line of sight – as are piloted airplanes? Join EE Times' Junko Yoshida as she moderates a panel of drone experts.