The POD is after the Dutch revolution, the Challenge is have Netherands incorporate Lorraine, bonus points is if the House of Lorraine or Habsburg-Lorraine rules the Netherlands.
After the Dutch revolution? That does make things hard.
Well maybe (a big maybe) if they decide to give the rhineland to king Willem I after the Napoleonic wars they also include Lorraine. To be fair you need a very different Napoleonic (and revolutionairy) wars for that to happen. Perhaps it would work if during the conquest of the Netherlands France decide to keep it instead of creating the Batavian republic (maybe they want to create one big happy republican nation), leading to the creation of an Netherlands in exile, the Dutch colonies lead by the stadholder. The allies decide to reward the Netherlands after the war with the Southern Netherlands, the Rhineland and Lorraine (the last also to punish France).
Another way I simply don't see happening. The Dutch republic had enough trouble partly because they didn't care enough) expanding into Belgium or north western Germany to be able to annex Lorraine. I don't think the Dutch Stadholder become duke of Lorraine would count as I never heard people say that Nassau was Dutch in the 18th century.
Besides that the house of Habsburg-Lorraine ruling the Netherlands seems unrealistic. I doubt the Estate-General would accept them as stadholders. Maybe they can conquer the Netherlands somehow? I somehow doubt they would able to do that.
