In addition to reductions in vortex drag, some of configurations mentioned here have desirable effects on structures, stability and control characteristics, vortex wake hazards, and other practical considerations.
The split tip design demonstrates that by manipulating the wake shape as well as the wing shape, some of the advantages of nonplanar wings may be obtained even with planar wings, and the possible applications of this idea warrant further study.
The C-wing configuration remains an intriguing design concept with many beneficial characteristics when applied to a large aircraft design. The implications of this approach remain to be more fully explored.
The direct insensitivity of ticket price to drag might be exploited as shown below. By redesigning an aircraft with fixed payload capacity, but with twice the floor space for each passenger, the fare would have to be increased by about $30 on a $300 ticket (see note). This is very reasonable, but might still be unacceptable in the highly elastic commercial transportation market. Nonetheless it is my hope that advances in aerodynamics and other disciplines can be employed to do more than just marginally lower the cost of air transportation, but rather improve its safety and comfort.