How about Korea or the Vietnam War? Or an alternate Cold War history where the Warsaw Pact and NATO went to war, ala "Red Storm Rising" by Tom Clancy.
Of course, I think Company of Heroes 3 should be in WWII. How many still untold stories and mistakes to fix. But if you go beyond. Then I would prefer:
- "Operation Unthinkable", this is an expanded World War II, many familiar and beloved units + those that did not have time for the war: IS-3, T-44, SKS-45, AS-44 and the continuation of Soviet assault rifles, Centurion, ARL-44 ... This is really great.
- "Caribbean Crisis", this is the closest moment when the WW3 could happen. And if you take the units, then there are no Main Tanks, a lot of missiles. It would be World War II on steroids. Early helicopters for infantry dropping. I think this is a great option.