  The recent advances in information and communication technology (ICT) have
further extended Internet of Things (IoT) from the sole "things" aspect to the
omnipotent role of "intelligent connection of things". Meanwhile, the concept
of internet of everything (IoE) is presented as such an omnipotent extension of
IoT. However, the IoE realization meets critical challenges including the
restricted network coverage and the limited resource of existing network
technologies. Recently, Unmanned Aerial Vehicles (UAVs) have attracted
significant attentions attributed to their high mobility, low cost, and
flexible deployment. Thus, UAVs may potentially overcome the challenges of IoE.
This article presents a comprehensive survey on opportunities and challenges of
UAV-enabled IoE. We first present three critical expectations of IoE: 1)
scalability requiring a scalable network architecture with ubiquitous coverage,
2) intelligence requiring a global computing plane enabling intelligent things,
3) diversity requiring provisions of diverse applications. Thereafter, we
review the enabling technologies to achieve these expectations and discuss four
intrinsic constraints of IoE (i.e., coverage constraint, battery constraint,
computing constraint, and security issues). We then present an overview of
UAVs. We next discuss the opportunities brought by UAV to IoE. Additionally, we
introduce a UAV-enabled IoE (Ue-IoE) solution by exploiting UAVs's mobility, in
which we show that Ue-IoE can greatly enhance the scalability, intelligence and
diversity of IoE. Finally, we outline the future directions in Ue-IoE.
