How about making it where you can train workers to be marines. Lets say 5 workers to become 1 marine and it takes 5 days to train. To make things better(worse?) you have to have enough biofarms to feed marines as well as workers. As the game is now, biofarms are only for workers and growth, the marines starve on the ships. This should make things more interesting to me if you get stopped from buying marines because you dont have enough biofarms, ie. cant feed'em cant have'em.
So if you decide to train 5 billion workers into 1 billion marines, if you dont have enough workers to keep the farms producing food you cant train/buy marines as you dont have enough food to feed them all.
Makes sense in my head but I think I forgot to type something down.
To make things even more complicated, if you are in negative growth for too long and your workers are dying, the workers rebel and start destroying segments.