Most projects don't fail because the idea is a bad one. They fail because the bulk cost in time, cash and energy is not worth the effort and the attrition.
Having worked with the same partners in those sectors for over a decade, this is not an impractical concept. It works in the air, ground and below ground level
... delivers letters and sells stamps. It runs fleets; both inbound and outbound. A post office is a bank, community center and a collection point. It's a hub.
Time is a design variable. Time is a dimension in which mistakes are discovered. So you design for the moment that someone says: "We need to change this."
The crux is that "vehicles" of any type do not address the needs of logistics - the primacy is handoff points, energy points, maintenance and human interfaces