There has always been discussion of secure bus service for short hop airport service to hubs. In a sense it makes sense. Two not inexpensive pilots and at least two not inexpensive flight attendants servicing an aircraft with a lot of Jet-A being burned. On many flights, the ground taxi time is as long as the en route time.
Instead you can have a single bus with a single driver.
It'd be ineresting to see how many x<100 mile routes there are out there these days.
PHL-ABE, PHL-MDT, CLT-GSP, CLT-GSO, CLT-CAE, ORD-MKE, DFW-ACT, and DFW-TYR all come to mind.