## 1 Introduction  
Virtualization is unquestionably the connective tissue that holds together all modern digital constructs of the fourth industrial revolution. It has become the transformational catalyst that enables the intangible segmentation of physical computational and networking elements and their consequently virtualized synthesis into dedicated softwarized implementations [1]. Next-Generation Networks (NGNs) emerged as an architectural body composited of current and cutting-edge technologies, capable of hosting a variety of services with diverse specifications. To ensure the effectiveness of such architectures, the integration of mechanisms with advanced administrative capabilities is of utmost importance. Virtual Network Embedding (VNE) was introduced as an innovative toolbox, seeking to efficiently administer VNs on physical networks. By exploiting exact and heuristic algorithmic techniques, VNE solutions handle the commitment of available tangible resources of Substrate Networks (SNs) to satisfy Virtual Network Requests (VNRs) and their demands [2; 3; 4; 5]. Since VNE is a mathematically complex problem, it is subdivided into the Virtual Node Mapping (VNM) and Virtual Link Mapping (VLM) procedures [6]. Subsequently, different objective functions can be applied on each subproblem for more customized optimizations. Depending on the approach, the chosen algorithms that contemplate the solution of the VNM and VLM subproblems handle them either separately or in some form of coordination [7]. The emergence of the Fifth-Generation (5G) communication system encouraged the development of services with diverse requirements, which were impossible to be accommodated by traditional mobile broadband architectures and management mechanisms. The needs in terms of performance, security, and reliability of vertical-specific applications were even more difficult to meet over highly heterogeneous network resources. As a cardinal response for service-centric embeddings, the Network Slicing (NS) operation was developed and endorsed by both academia and industry [8; 9; 10; 11]. The foundations of NS are rooted in the Software-Defined Networking (SDN) and Functions Virtualization (NFV) designs, enabling Virtual Network Operators (VNOs) to flexibly operate the instantiated VNs. Each NS-oriented resource allocation corresponds to an independent slice of end-to-end (E2E) networking elements, customized for satisfying VNRs with explicit requirements. The virtualization-based concepts of NFV, SDN, and NS are vital for the successful realization and programmability of NGNs and are well received by all involved entities [12; 13]. Fifth-Generation intended to support the heterogeneous requirements of Ultra-Reliable and Low-Latency Communication (uRLLC), enhanced Mobile Broadband (eMBB), and massive Machine-Type Communication (mMTC) [13; 14]. However, the conceptualization of the Internet of Everything (IoE) ecosystem triggered a subsequent need for fundamental changes [15]. Particularly, the architecture of eMBB posed as a dominant trend for supporting Next-Generation (NG) services, but ultimately the design of 5G technologies proved ineffective as the key IoE enabler. The shift toward supporting and serving the ever-increasing number of connected users and devices in the context of new and exciting applications appears to be inevitable. Thus, one of the greatest challenges that 5G faces is the transition from a service-centric application design toward a user-centric one. It seems unlikely that 5G will ever be able to fully accommodate immersive NG catalysts such as eXtended Reality (XR), Brain-Computer Interfaces (BCIs), and haptics in the service of sensitive applications such as telemedicine, manned and unmanned aerial vehicle navigation, and interaction of autonomous systems [16; 17; 18; 19]. The task becomes even more complex since these separate ecosystems are intended to inter-connect and communicate, forming Cyber-Physical Systems (CPSs) over NG telecommunications infrastructures [20].