How about a little easter egg? In this case, one side quest for find a treasure chest defended by a new npc, player should dialogue with it and outcome of dialogue would bring (1) a fight against a hero or (2) a safe reward without chest gain, player options to deal with npc. Quest is not related to any faction and should be hidden enough in map to be classified as a easter egg, so its a joyful prize for map explorers only.
I take it you don’t have 100% Quest completion on Ultimate