BPON, EPON, GEPON, and GPON have the same basic wavelength plan and use the 1,490 nanometer (nm) wavelength for downstream traffic and 1,310 nm wavelength for upstream traffic. 1,550 nm is reserved for optional overlay services, typically RF (analog) video.
Not sure it's usually referred to as WDM especially as without the optional wavelength there's only a single transmission wavelength each way. Certainly WDM-PON is a different thing to the above.
The ONT is the consumer end and it has to do the demultiplexing.
Passive optical devices can split and combine wavelengths or be directional.
MaxDSL - goes as fast as it can and doesn't read the line checker first.