As far as Brotherhood DLC content goes, it would be kind of nice to see us be tasked with heading a *commonwealth* chapter of the Brotherhood as the Prydwen plans to move back to its base of operations in the citadel. The Brotherhood doesn't plan to keep its main force in Boston forever, and after the main quest is over, your held at the highest rank possible below that of an elder. So.. becoming the elder of the brotherhood in the commonwealth would be kind of great.
You could pick who you wanted to stay, like Haylen. potentially find a way to bring Danse back in to the fold, which would make him pretty happy. You certainly wouldn't have the great explosive force anymore like you did with Maxon, but hey a couple of vertibirds, and a dozen soldiers to start would be a great point for breaking ground. This would also be a good way to make settlements have a brotherhood allegiance instead of minutemen. (something I've wanted to be able to do.)