Suppose France delivers a defeat on Prussia that is so demoralizing that the fates of France and Prussia are almost reversed - that is, Wilhelm I is forced to abdicate, and perhaps the House of Hohenzollern is forced to flee the nation.
I don't care HOW France accomplished this (considering a French victory of this kind is unlikely given OTL scenario), I would like to see the form of the world after this war. These are my thoughts.
France would gain territory, or at least a sphere of influence, in the Rhineland. Perhaps an annexation of Luxembourg, after Napoleon III's first failure, seems reasonable.
Speaking of Napoleon III, he would remain in power, though the same could not be said for Wilhelm I and/or Bismarck. After the war, there would certainly be a shift in policy in Germany, probably not a "Berlin Commune", but still a significant change.
This said, Germany would not truly unify - perhaps Prussia is so badly broken that regions of micro-influence, such as Bavaria upon Württemburg, could occur. While the Confederation may not break entirely, the German nation would be even more federal than it was.
With France remaining the main continental power in Europe, and French colonialism and expansionism remaining Britain's enemy, I could see World War I being between Britain and France, with Prussia/Germany obviously backing Britain here.
It starts to sound like a Germany screw here, but what does everybody else think about this? What are your thoughts on such a huge French victory?