As for security issues, that's just another reason why more prevalent surveillance is not necessarily a bad thing. I suspect air transportation will become more commonplace, but before that occurs, we will see an influx in public transportation and automated (driverless) vehicles. Technically, someone could hop in a private plane and fly over national borders now. Radar, flying surveillance drones and other ways of monitoring airspace would have to become more commonplace.
Also, there is the possibility that in controlled or restricted areas, your vehicle's (or your suit's) navigation systems will be overridden by a local flight control system, to ensure that travel through that airspace is as safe as possible. The ubiquity of local air travel may largely depend upon the feasibility and reliability of these systems. There is also the inevitability of redundant on-board anti-collision systems that are already being implemented in driverless cars. There are many unforeseen changes to the national security and air traffic control infrastructure that will shape the emergence and the availability of personal air travel.
It's quite possible, that between radar, surveillance drones and other methods, that we may be able to know what's going on in every inch of a nation's airspace at anytime, and thus, be able to detect any unauthorized vehicles. Flying transportation could be limited to state-controlled, automated, public transport and privately chartered drones. We may never see the cliched sci fi city, dense with personal flying vehicles. But, that won't change the technological inevitability of their invention. Public ground transportation may become so efficient that they would be considered a wasteful luxury.
Even if the flying car doesn't become a ubiquitous consumer item, you can be sure that we will see advances in short-range, maneuverable, VTOL transportation in both the military and commercial sector. Personal flight systems are one natural evolution of this, even if they are relegated to military, public safety, and extreme sports usage. Everybody may own one, but whether or not we will see them in densely packed cities depends on how efficient the safety measures will be.
Edited by zen_mutiny, 09 May 2013 - 08:57 PM.