Currently, players can travel by spending movement stamina or oil barrels to any region in the map. No other restrictions.
Let me suggest an additional resources utilisation for this: Visa papers (Just the papers made from wood).
Individual players don't consume papers at all. Paper companies only have government clients.
The wood and paper dropped from cases are considered trash (even the game mocks us when 100 wood drops).
The game has unlimited wood theory, but seldom put to much use. The movement update changed the petroleum industry for good. So, along with the other plans for the next update, Visas can be added too.
The visa papers are spent to travel to any regions ruled by a single country.
If a region gets occupied by another country, the players who don't have the visa to the new country shall not leave, implying special immigration zones like airport gates and refugee camps.
Individual players uses more paper and wood.
More companies in the paper industry.
Paper drops from cases will have more value than just trash.
More realistic movement than the hysterical free jump to regions.
My next article for update suggestion "Diplomacy Score" and "Passport strengths".
More complicated like the real immigration politics.