I actually really like this. A Pearl Harbor start date has every major power involved in the war, and at a time where it isn't as clear cut as to who will win.
Starting in 1939 (vastly more so if you start in 1936) as Germany, it's never in doubt that Poland will fall quickly, and it's fairly cut and dry when BENELUX and FRA fall as well (and DEN/NOR). The game really sort of begins when you attack the USSR, because the USSR is the only continental power that can arrest the advance of a human Germany.
A player-led Barbarossa is almost assuredly going to be a victory, so starting in the depths of December once the German advance has been halted really poses a lot of interesting challenges for a player. Throwing a player straight into a stalled Barbarossa would make for a really fun game.
And, of course, the infamous 1945 start date would be welcome

. The desperate defense of the Reich is something every HOI player needs to experience!