I was thinking, it could be plausible a scenery where in the French-Prussian war aftermath, Bismarck could agree to leave Alsace and Strasbourg to the French and take instead Lorraine in full as warprize, or in the interval between said conflict and WWI after long deliberations, Germany and France agreed to a land swap (return of Alsace in exchange of concession of Lorraine)? I post the thread as AHC because, maybe it could be interesting to formulate some possible alternative proposals...