I recommend to my friends who are going to commute that they bid the 75/76 exactly for the reasons pointed out. The flexibility to move about inside the system (primarily domestic to Z) could prove invaluable for a commuter. Personally, I think the trips are ever so slightly better on the Bus than domestic 75/76. I haven't looked at it recently but I think the Bus reserve utilization is lower (at least recently). So for those moving to SDF, I recommend the Bus.
There is extremely little hope, practically zero, that we would ever see additional A-300s on property and we are growing the 76 fleet. The 76 is still in production, is a known quantity, and requires no additional training footprint. An overnight solution to lift shortage when you can get your hands on one. All that to speculate that UPS will continue to seek opportunities for further expansion of the fleet.