As others have stated, extending the timeline so Germany could start the war somewhere between 1943-1945 when Hitler thought Germany would be ready, would be really nice. Also, leaving enough time after Germany is defeated for the Allies to potentially go to war with the Soviets. And I've personally always thought the Korean War should have been included in HoI3 as it was in HoI2, so extending the game to 1956 or so to give it a few extra years in case it lasts longer would be ideal. There were other conflicts that took place shortly after WW2 that should be included as well.
The First Indochina War, the Greek Civil War, the Indo-Pakistani War, the Arab-Israeli War, and other smaller conflicts like the Indonesian National Revolution, the Malayan Emergency, the Mau Mau Uprising. There was a surprising amount of small conflicts after WW2, with the decolonization leaving a lot of unstable or unpopular governments and communism trying to take hold where it could.