How plausible would be knocking UK from war before december 1941? It doesn't mean that UK would have to surrender, just make Brittain ask for peace.
A) a pretty minor POD. Lack of successes in Africa? Slightly more successful Kriegsmarine?
B) major one/borderline ASB. Fall of key fortress like Alexandria, Malta or Gibraltar (or worse... All of them)? Failing to stop Blitz?
C) ASB as Sea Lion