Making an electric car isn't exactly easy, but the realm of things it's not as difficult as space flight. Musk and his company has also recently made impressive strides in private spacecraft with the Dragon capsule docking with the ISS. Musk has recently made it known that he's also planning a supersonic, electric powered hovering jet plane.
I'm no aeronautical engineer, but that sounds even more difficult than creating a spacecraft. The announcement came when Musk was talking about some of his plans for the future. He stated that he was considering whether it would make sense to create a parent corporation to own stock, presumably in an aircraft manufacturing company. The comment was made to the automotive website Jalopnik and Musk admitted that he wasn't sure if it was feasible or sensible, that he was only considering it at this time.
It's worth noting that aircraft able to take off and land vertically are difficult to maintain and create. There are only a few jet aircraft currently capable of taking off and landing vertically and all of them are military aircraft. The new F-35 Joint Strike Fighter has a version that will land vertically but requires a short runway to take off. That aircraft has been plagued with failures in critical components supporting vertical landings.
One true vertical landing and vertical takeoff jet is the Harrier, still being used by both British and American militaries to this day. However, that aircraft isn't considered supersonic. Battery packs would have to, very long way to be able to power an aircraft exclusively. Presumably, Musk is likely talking about some sort of hybrid aircraft. It will be interesting to see if Musk moves on with his plans for an aircraft.
[via The Register]