I see Alsace-Lorraine actually as one of the toughest nuts to crack. For the German side, losing it defines a lost war. For France not winning it means admitting the impossibility to win against Germany and to accept that Alsace-Lorraine will have to be forever given up (which the repulic mostly wasn't ready to).
The only realistic idea would be some sort of plebiscite under conditions which give both Paris and Berlin not the impression that the result is a risky toss-up (or bound to lose)... but which gives both sides the illusion that it will grant resp. confirm possession of Alsace-Lorraine.
A somewhat smaller chance might be that both sides accept a limited plebiscite which is more or less designed to split off the definitely French-speaking areas mostly in Lorraine. This would result in the French Government being able to show some gains in the matter, whereas Berlin could sell this agreement as a principal acceptance of the German character of the remaining Elsaß-Lothringen while the Reich only got rid of the untrustworthy Wackes which would never be reliable Waffenbrüder anyways.
The only realistic idea would be some sort of plebiscite under conditions which give both Paris and Berlin not the impression that the result is a risky toss-up (or bound to lose)... but which gives both sides the illusion that it will grant resp. confirm possession of Alsace-Lorraine.
A somewhat smaller chance might be that both sides accept a limited plebiscite which is more or less designed to split off the definitely French-speaking areas mostly in Lorraine. This would result in the French Government being able to show some gains in the matter, whereas Berlin could sell this agreement as a principal acceptance of the German character of the remaining Elsaß-Lothringen while the Reich only got rid of the untrustworthy Wackes which would never be reliable Waffenbrüder anyways.