This idea is a new one, that I have enver tried in game, but it could be interesting.
Base of thinking : some units are not really used, because they upgrade to fast. Especially with extended unit lines.
Easy solution : make them upgrade slower.
Here is my idea. Let say the unit line for aircraft is
Biplane (1920s) - Fighter (1940s) - Jet Fighter (1950s) - Jet Fighter II (1960's) - Modern fighter (1980s) - Advanced fighter (2000s)
The idea is to make biplane upgrade to jet fighter, fighter to jet fighter II, Jet Fighter to Modern figther, etc....
So, when you discover a new techs, you must actually build your new units, and keep the older one in your army. You can upgrade them only when they are really obsolete. It would also reduce the "attack with 20 newly upgrade modern armor just after we discover the tech"
Of course, this would be used mainly for the most modern units, with 1 turn = 1 year.
Base of thinking : some units are not really used, because they upgrade to fast. Especially with extended unit lines.
Easy solution : make them upgrade slower.
Here is my idea. Let say the unit line for aircraft is
Biplane (1920s) - Fighter (1940s) - Jet Fighter (1950s) - Jet Fighter II (1960's) - Modern fighter (1980s) - Advanced fighter (2000s)
The idea is to make biplane upgrade to jet fighter, fighter to jet fighter II, Jet Fighter to Modern figther, etc....
So, when you discover a new techs, you must actually build your new units, and keep the older one in your army. You can upgrade them only when they are really obsolete. It would also reduce the "attack with 20 newly upgrade modern armor just after we discover the tech"
Of course, this would be used mainly for the most modern units, with 1 turn = 1 year.