I would be interested to see some kind of pre-war/post-war story based dlc, where your character discovers the location of a top secret vault while browsing through a terminal in the Vault-Tec Regional HQ. The vault houses the top Vault-Tec scientists from the pre-war era, having suvived by having their consciousness transferred into robots, so that they can continue their long term goal of observing the experiments in the other vaults. They have continued to science it up since the bombs fell, and unlike the scientists from New Vegas' Old World Blues DLC, kept sane through the use of simulations. Upon entering the vault (which requires that you wear no power armour), we are met with waves of overwhelming robotic security, and are ultimately subdued through the use of a tranquilizer gun (which will be obtainable at some point, and renders NPCs temporarily unconscious). We wake up inside a simulation, in our pre-war bed beside our spouse, and for a short while you live the life of a normal person, exploring some of the world before the world went to hell. This is a good chance for us to learn more about the Fallout lore and improve upon the backstory of your character.
Through your actions and dialogue, you can affect the stability of the simulation. You can choose to accept it as your new reality, and stay with your spouse and child, or you can reject it and continue to destabilize the simulation until your spouse winds up getting murdered... Again. Upon witnessing your spouse being murdered again, fake or not, is enough of a shock to eject you from the simulator, while if you chose to stay in your perfect dream world, your current romance/bestest friend(s) has come and shut down the simulation. Through some dialogue we learn that we unleashed enough devastation for them to either sneak/fight their way through to where you were (dependent on if they are good fighters or not), and that we have been gone for weeks/months. Also if Danse comes to save you, he has no power armour on, because we weren't allowed to have any. Or maybe he does have his armour, and we have a laugh when we are leaving about how he had to blow the enterance bigger with a mini nuke or something. Whether you got out of the simulation yourself or not, good for you, time to raise some hell. Fight and loot your way through the facility, learning more about what the other vaults were used for as you go. One of the scientists begs you to spare his life (optional) and in return you gain him as a follower. Whatever settlement he is stationed at gains a bonus of some kind, perhaps laser defence turrets do 50% more damage. The vault is littered with unique, pre-war style weapons, armour, and power armour pieces. Power armour pieces could include modified T-45, T-51, and T-60 parts with dual mods on them, i.e a Targeting Rad Scrubbing T-51 Helmet. A few single prototype pieces like X-03 legs, X-08 Torso, X-04 arms, and a full set of X-09 armour, all with new, unique mods on them (thermal vision plz?).
P.S.
I apologise for my poor writing skills...