1/Is the Etha 3 M replacing the Emek?
No, the Etha 3M is more of an "Emek Pro" if you will, the standard Emek 100 will still be available, the Etha 3M however will come with more high end features already installed from the factory such as a adjustable aluminum trigger, a aluminum feed neck, a 2pc barrel, and the FL valve already installed.
2/Is the Etha 3M PALs compatible?
Although you can put a PAL hopper on the Etha 3M, you will not see the benefit from it as the Etha3M does not feature a PALs feed neck.
3/Is the Planet Eclipse Etha 3M worth it over the Emek100?
The Etha 3 M is simply designed to be a higher end option than the Emek 100. They are going to be very similar markers all in all, however the Etha 3 M is going to feature multiple things that people commonly upgrade on the standard Emek 100.