This Boeing experience seems very interesting to me. This octocopter is the biggest I've seen. I estimate that the propellers should be about 2100mm.
I ask some questions about whether this really makes sense:
Batteries and flight time: 7 or 15 minutes is enough?
This prototype could fly 7 minutes with 227kg and about 15 minutes with 100kg, according to my calculations.
Perhaps this short flight times have non sense but, if it could flight for 50 minutes with a lighter payload? it is possible and they say than they want scale it. 100 or 200kg for 50 minutes? this could replace helicopters in some missions.

But the question now is this:
Do multicopters have size limit?

Many times it has been said that large propellers do not achieve stability and multicopters can not be scaled up, but some recent examples deny this theory.
big propellers have more inertial but aircraft have also more inertia so it need less response time to get stability. So Are there propeller size limit?
Some time ago it was said that the limit was 26-28 inches, but now you can see multicopters with propellers of 1500mm with good stability, so Can we see fixed pitch propellers of 3 or 5 meters?

Known specifications:
MTOW - 747 lb  (340 kg)
Payload - 500 lb (227 kg)
Dimensions: (4.57 m) by 18 ft wide (5.49 m) by 4 ft tall (1.22 m)

Assumptions:
Propeller 84 "
Battery = 40S 40Ah 148V (li-ion)
Battery weight - 40kg total
Empty weight (no payload, no battery) - 70kg

Thanks, Josip Nunth