The labor- and money-saving efficiency of a private jet makes the decision to own and operate one similar to deciding to buy a new CNC machine or an integrated computer system.
One way to increase the efficiency of a high-bypass jet engine is to turn the fan into an open rotor, a bit like returning to propellers, but using two rings of stubby counter-rotating blades.
The design of jet engines has progressed over the decades, but has been stuck for many years in a plateau where efficiency gains have flattened out to only .5% a year.