From years i read how peoples want end game content.
There is my idea…
New mechanic conquering,defending re conguering few main citys.
New type world bosses with high dmg ,aoe abilitys high dmgs.
These new world bosses will spawning after for an example 30,50 ,100 times all Lair Bosses.
That mean will be new mechanic all the time displayed ,count how many times are killed Lair Bosses. Whenever everyone players kill ,50,100 times all Lair Bosses,start this new type art desigh bosses,these world bosses will start attack all main citys which want kill all npc’s inside citys and these new new type world bosses would have masive a lot monster which follow them and kill everything in his path .
Whole idea is players defending all main citys and all npc’s will be stoped working(not allow of us players to work with them).