Ok, i have now an idea to be possibly implemented in scenario editor.
What about have the option to enable production in some cities only certain turns?
Let me explain a simple example: USSR's winter events to WWII.
Winter is every 8 turns, then, only each 6 turns we can produce the units in that city. I know that in the current editor there are a way to do this, so that imply repat the unit n times (for example, if u wish ur WWII to least 75 turns, u'll need 75/8= near 8 clones of the unit u want to be produced in that turns.