This will probably be tossed into the AE4 pile, but I think that, similar to the Open Skies allowance in the EU starting in 2001, there should be an allowance for airlines to fly within and between certain countries to simulate the geography of the Cold War, where there was no Montenegro or Slovenia or Kyrgyzstan or whatever--just Czechoslovakia, Yugoslavia, and the USSR.
This "Cold War geography" would be in place from the earliest game year until game year 1991. Afterwards, all operations outside your base country will be terminated--e.g., an airline flying in the USSR with its base in Tbilisi would lose all routes that didn't have a start or end in Georgia. You would keep your aircraft, but they will gain hours or go idle.
These would be the route allowances:
For Czechoslovakia: Open skies within and between Slovakia and the Czech Republic
For Yugoslavia: Open skies between and within Croatia, Serbia, Montenegro, Macedonia, Slovenia, and Bosnia and Herzegovina
For the USSR: Open skies between and within Russia, Armenia, Azerbaijan, Belarus, Estonia, Georgia, Kazakhstan, Kyrgyzstan, Latvia, Lithuania, Moldova, Tajikistan, Turkmenistan, Ukraine, and Uzbekistan.
Yes? No?