I always liked the idea where you had epic, world events that incased say an entire world. Like tatooine for instance. A complete *****torm invasion at epic scale. 1,000 aliens marching across the planet killing or taking over. 100s of npc's and a pvp feel where you could go and participate and help turn the tide, save a town, kill an epic boss. Just by being there, you were included in the raid. No guild politics, no lfg waiting room, just simply go to the planet and you're in. The more you participate and the more you contribute, the more reward you get. This is how I see end-game raiding on a large scale. This would be content everyone could see and participate in, not just the small 4% of super nerds.
It would be exciting to have 50 guys racing across the plains to attack an oncoming wall of armies npcs and players alike.
Throw in some war machines, cannons, ships flying overhead, explosions, environment of a warzone. Sweet!