Beth, as you say, could have done this. They were half way there with the Billy Peabody mini-quest. Here's how I am envisioning things: After some time fixing up Somerville, the kids old man could relate a sad tale to you. He'd bemoan losing his love and mother of his children in the Quincy massacre. He would say that in his heart he knows she is still out there, captive to the gunners. Track her down, kill all the gunners and bring her back alive, unlocking the ability to create settler companions. Other means of unlocking to be available of course. At first I thought this was a silly idea. Now I'm more sure about it.