This work elaborates on: i) why the sliceable bandwidth variable transceiver (S-BVT) represents a key enabler for nextgeneration optical metro networks; ii) how it should be designed to take benefit of its capabilities and advanced features; and iii) which are the promising technologies to be adopted addressing the most relevant requirements and challenges. Specifically, S-BVT architectures based on multicarrier modulation and flexi-grid technologies, adopting cost-effective optoelectronic front-ends, enable flexible adaptation to dynamic traffic and variable path condition, targeting high capacity and scalability, while saving network resources and costs. Programmability and modularity are envisioned for integration in software-defined optical metro networks.