I was thinking about adding a new reinforcement sistem thanks t the triggers in game.
As you know, there are 2 Forgotten Campaigns, 1 under Nod control and 1 under GDI Control

Nod Forgotten
During the Nod Forgotten missions, you may find a Nod Radar, if you capture it, you will alert Nod Reinforcerment in your area, making them at your disposal.
That mean, if you start a mission with Engineers, you have to keep them in safe, because the Forgottens CANNOT train Engineers.

GDI Forgotten
Here the reinforcement work different. GDI never deal directly with the Forgottens, but if they are in the area against Nod, thy may help you.
The Casualities Sistem let GDI send waves of reinforcement, as they lost units.
Ex: If GDI loose 30 units, GDI HQ send APC loaded wit infantry, if they loose 50 units, they will send a few Titans and Wolverines...
GDI Reinforcemnt cannot be controlled.

Hope triggers let me do that!