As mentioned before, there is no real need as aircraft can already fly as long as duty hours permit. Air Forces do it in fast jets because they burn their small quantities iff very quickly or because their transports (which are not capable of the range of todays modern equipment) need longer time on station (eg AWACS, etc) or very long range using multiple crews. Remember that the military pilots are exempt from CAA style flight time limitations. In fact their pilots do not hold licenses.
The cost of inflight refuelling would be vastly greater than the cost of stopping off at an airport and picking up gas.