Who in the US military would be interested in some kind of wacky hover-car plan?
The TX should be able to cover 250 miles on a single tank of fuel, using a combination of flight and ground movement: DARPA have specified several desired mission plans. One, for instance, would see a TX lifting off from a foward base in Afghanistan and flying 60 miles to leapfrog over the belts of mines, booby-traps and roadside bombs which typically encircle such bases. It would then carry out a 100-mile patrol on the ground, enabling its occupants to stop and talk to people, set up checkpoints etc, before hopping back across the minefields to its base.
Other mission plans would see TXs flying themselves ashore from ships at sea, carrying out medical evacuations, or stealthily resupplying covert special-ops teams by landing and driving the last part of the route. DARPA specify that the TX should be "at least as quiet as a conventional automobile" when driven on the ground and as quiet as "a single engine helicopter in flight mode".
DARPA projects need to be at least nominally aimed at fulfilling a military task for one of the US armed forces, and in this case the hook on which TX is hung is the US Marines' recent concept of "Enhanced Company Operations" or ECO. The Marines are much more broadminded about wacky hover aircraft concepts than the other US services - they have been a major force in the development of jumpjets like the Harrier and the F-35B, and are the primary users of the amazing V-22 Osprey tiltrotor - so they're probably a good fit for this.
The idea of ECO is, put simply, to let rifle companies* operate more independently by giving them more of the tools normally found attached to larger formations like battalions and above. This can make a lot of sense in modern wars where a company commander and his people may find themselves far from their battalion/battlegroup HQ and its specialist supporting units, yet responsible for a big area.
Previous ECO initiatives have given US Marine company commanders their own intelligence cells, and let units as small as squads have over-the-horizon comms, close air support and other things which would normally be found only at bigger headquarters.
ECO proponents would also like a Marine company to be able to have its own air mobility, in particular for logistics and casualty handling and for such purposes as moving from ships to shore. So far this sort of thing has always been done using helicopters and Ospreys, but by their nature these machines can't really be company-level equipment: they are huge and manpower-intensive, such that a detachment of a few choppers would often be accompanied by more personnel than a rifle company has altogether and would be commanded by an officer at least equal in rank to the company commander. Every Marine aircraft at the moment is piloted by a wings-on-chest officer.