I had an idea that I was working on for another 2-6 month session MMORTS that i think is valid here as well
What if as we start to wind a galaxy down, we have a Mass Effect Reapers event? Really powerful alien ships come in from across the galaxies edge and slowly wipe out players and destroy star systems over time. each super-powered alien fleet destroyed is worth a ton of galactic emperor points.
an alternate start point is a wormhole at the center of the galaxy that spews out these alien fleets and a “death star” style planet. if you can stem the tide and destroy all the fleets protecting this death star solar system and invade/blow up the death star object. you “win” the game.
this allows for clearing players out of an old galaxy and is a final challenge for the surviving players. could be interesting?