I'd be intrigued to see what would have happened had part of Wilson's fourteen points explicitly called for no territorial changes without the will of the people being ascertained through fair, internationally supervised plebiscites.
Those plebiscites that were held have given us a glimpse of what might have happened. In the biggest example, that of Upper East Silesia, Germany won the vote with almost 60%, from a population that was a slight Polish majority. Probably about 35% of ethnic Poles voted for Germany, and a good question is, could Germany have counted on similar support levels from ethnic Poles had other Plebiscites been held in the Posen, West Prussia, and future Polish Corridor regions.
Of course Alsace Lorraine would have been an epic electoral battleground. Assuming an overall French victory, I'm wondering if certain parts of Alsace would still have voted for Germany, similar to how Germany lost the vote in the Northern plebiscite zone of Schleswig, but won the southern portion.
Anyway, I'd be interested to see other people's take on this.