My best friend just mentioned to this me actually.
I don't know exactly why they were removed, but I'm not sure if the system in place still exists for this. I know the mods have the ability to change galaxy settings but I think custom galaxies were a little more than just adjusting galaxy options. In any case, I can't find reference to them anywhere in the code so it's possible that they were removed from the game entirely.
I agree though, this would be a welcome (re)addition. I think some details would need to be ironed out though, so maybe this is a good opportunity for doing just that. What do you guys remember about the custom galaxies? The biggest thing I remembered was very small and organized team based games. Stuff like country vs country, mw players vs andro players, that kind of thing.
I guess to ask it a different way, what would you like to see in a custom game that makes it different than "just another galaxy"?
Got a few bucks? The Imperial Tip Jar is accepting contributions!