That's very interesting. What are current (commercially viable) alternatives to electric drones?
The larger ones tend to have an electric generator to power the control surfaces, smaller drones tend to carry a battery for that and use the engine solely for forward propulsion.
This is for fixed-wing only, so it would apply to Zipline P1 but not P2, by the way. There have been some engine-over-electric setups to run multirotors from a single powerplant, but it's generally awful. It may or may not work for hybrid architectures like a quadplane, or a single-engine-VTOL like a tailsitter, all these things are in active development.
Longer term it’s more debatable but we hand waving delivery drones as completely pollution free when we don’t know what from they would actually take is simply wishful thinking.
Zipline 2 has a 10 mile range and is VTOL though they’re aiming for a long wire for delivery rather than landing. https://en.wikipedia.org/wiki/Zipline_(drone_delivery_compan...
Zipline 1 does have an 50 mile range but it isn’t VTOL they use fixed wing and have a launching system and a net to catch drones. Packages are dropped at 100 feet requiring a parachute and a 5 meter wide landing zone which makes it undesirable for large scale adoption.
Pollution wise you need to consider the lifecycle of a drone which is likely far worse than a van. Many drones are using very dirty small internal combustion engines. Safety wise replacing 1 van with 30+ heavy drones each traveling far more could easily favor the van.