How about a DLC where:
-Preston Garvey tells you a fully detailed story about Quincy Ruins and the events that took place.
-A flashback which the player (as a Minuteman who fights along side Preston) is in Quincy and his/her action affects how Preston tells the story.
-The player eventually falls in battle as Preston escapes.
-After the flashback ends, Preston makes a request (QUEUE THE FALLOUT THEME SONG) to take back Quincy Ruins alongside the Minutemen. (If any named Gunners were killed prior to this DLC, they will be replaced with other named Gunners who can be interacted with to at least characterise who the Gunners were)
-After Quincy Ruins has been successfully recaptured, it can become either become a new settlement which the player has full control of, or ends up like Diamond City.
-Preston will walk over to where the player-controlled Minuteman died and mourn.?