I have a few ideas with 3 variations:
1) One solution to do this could be to increase infantry upkeep to prevent excessive infantry spam
2) Increase the upkeep of upgraded squads with schrecks, PPSh, LMGs and the such.
3) both of these
Why?
Because currently even making 10 basic infantry squads (volks, conscripts, grenadiers) has nearly no impact on your upkeep and you don't need to worry about it. That's one of the reasons why it's so effective to spam infantry. By introducing more upkeep there would be a downside to this, currently there's hardly any downsides to infantry spam. This should also apply to excessive support weapon spam.
It could be done in a way that having too many units of the same type/class (basic infantry / support units) would cause extra upkeep. This way we wouldn't get a situation where a good combined arms army would receive a huge upkeep penalty because it consists largely of different types of infantry units.
Basically this would bring more strategic depth to the game and make it far more interesting instead of facing the same volks, PPSh or LMG gren blobs every game. At the same time it would improve the skill factor and competitiveness of the game. At least in my opinion.
