The retail industry is already facing an inevitable transformation worldwide, and with the current pandemic situation, it is even accelerating. Indeed, consumer habits are shifting from brick-and-mortar stores to online shopping. The bottleneck in the end-to-end online shopping experience remains the efficient and quick delivery of goods to consumers. In this context, unmanned aerial vehicle (UAV) technology is seen as a potential solution to address cargo delivery issues. Hence, the number of cargo-UAVs is expected to skyrocket in the next few decades and the airspace to become densely crowded. To successfully deploy UAVs for mass cargo delivery, seamless and reliable cellular connectivity for highly mobile UAVs is required. There is an urgent need for organized and connected routes in the sky. Like highways for cargo trucks, 3D routes in the airspace should be designed for cargo-UAVs to fulfill their operations safely and efficiently. We refer to these routes as 3D aerial highway. In this paper, we thoroughly investigate the feasibility of the aerial highways paradigm. First, we discuss the motivations and concerns of the aerial highway paradigm. Then, we present our vision of the 3D aerial highway framework. Finally, we present related connectivity issues and their potential solutions.