Considerable research is being conducted to exploit the potential of novel WDM-PONs exhibiting individual, data and protocol agnostic virtual point-to-point (p2p) links for each ONU. The research focuses on the deployment of uniform building blocks throughout the entire access network and on upgrading the channel data rate efficiently towards 10 Gb/s. This contribution gives an overview of basic principles of WDM-PONs, discusses merits and drawbacks of related approaches and highlights important requirements for key components such as injection-locked Fabry-Perot lasers, (R) SOAs, SLEDs and athermal AWGs.