Let me start by saying that this suggestion is very much inspired by the Erchius EPP mod. Which, while is fine as a mod, I think it would be a cool thing to have in vanilla as an endgame item. I believe it would make EPP progression feel more complete, rather than just abruptly end on the Cooling EPP. By the very end of the game, once you've explored every other planet type, you would finally be able to harness the moons as well. Make it require hundreds of liquid erchius fuel, crystal erchius ore, as well as dozens of phase matter and solarium stars and I'd say it's fairly balanced out.