This house rule is simple: allow the construction of new industrial complexes.
You can play with that rule only or use one of two alterations to the rule.

1. Only allow new industrial complexes in specific territories. Territories that may be considered industrializable. For instance: France, Poland, Norway, Finland, Greece, Hungary, Egypt. The territories
would be determined before the game begins. Additionally, as with Axis & Allies, players would only be allowed to place industrial complexes on territories that they have held since the begining of the turn.

2. Only allow new industrial complexes in territories that a player controlled since the begining of the game. In other words you can only place a new idustry on territories with your country's color or shade.