The standardization effort targeting 10 Gbit/s EPON systems, together with the requirement for coexistence with the legacy IEEE 802.3ah compliant equipment, impose a set of very tight requirements in terms of wavelength allocation plan for future EPON systems and significant limitations in terms of triplexer design for Optical Network Unit (ONU) modules, where 2 wavelength channels (or 3, when an analog video overlay is used on the downstream) must be properly separated with minimum power and quality loss, providing also a high quality transmission window for the upstream 1310 nm signal. In this paper, we look closer at the possible triplexer and filter design for emerging 10 Gbit/s EPON systems in the light of current IEEE 802.av Task Force activities and technical limitations of the Wavelength Division Multiplexing (WDM) filter design process.