From what I understand of the WW2 campaign, any modern version would call for large spaces, so preferably large countries, right?
I mean, if you're rolling a probability of encounter based on an 'Enemy Threat Level', better have the place of looking for the enemy rather than having it sitting in the middle of the FOV like an elephant in a phone booth?
E.G. in case of a Chinese invasion of Taiwan, chances are that the enemy threat level will be busting the 100% all over the map...
So China vs India sounds fine, or China vs Russia or India vs Pakistan...
Or something more Middle-Easty, just for the originality of it, y'know
Like Egypt vs Libya, Egypt vs Sudan? Iran vs Saudi Arabia? Iran vs USA
in Saudi Arabia?
By the way, did you plan making this a 'combined arms' campaign, with different players controlling different types of units (e.g. one with a tank squadron, one with infantry, one with airborne forces...)? Just a thought.