Creating the F-35U is made easier by the fact that all the controls are already electronic, and contain a lot of automatic (robotic) flight control software. Engineers probably noted how close, in design and purpose, the innards of an F-35 were to the various combat UAV designs going around. A robotic F-35 is envisioned as an unmanned bomb carrier, although there is nothing to prevent the F-35U from being able to fight other aircraft. For this, it would either need the high-performance AESA radar, or be able to use radar data from a piloted F-35 (or other aircraft.) This sort of "networked" air battle is already a hot topic in the U.S. Navy and Air Force. It would also be pretty easy to create an F-22U. Both the F-35U and F-22U would have a major advantage over manned fighters, in that a robotic aircraft could perform rapid maneuvers that the human body could not tolerate.
In an attempt to gain an edge in the coming unmanned combat aircraft market, a pilotless F-35 has been designed. Manufacturer Lockheed-Martin is currently devoting about a third of research and development money to unmanned vehicles, and the pilotless F-35 is a small part of it. This F-35 project has been underway for about two years now, and is a private effort, not part of any government contract. While the F-35U (for UAV) would weigh less (no cockpit or life-support equipment) and carry lower tech sensors (instead of the expensive AESA radar), it is expected to cost the same as a manned version. In other words, about $40 million. But the lower weight would enable it to carry more weapons (perhaps up to ten tons).