This problem doesn't have to be solves with warehouses. Drones are a solution to the last mile problem. Simply make delivery trucks into mobile drone launching

This problem doesn't have to be solves with warehouses. Drones are a solution to the last mile problem. Simply make delivery trucks into mobile drone launching platforms and then Amazon or UPS can drive into a neighborhood and drones will deliver all the packages light enough and the driver will deliver all the heavy ones.