OK, I've squeezed just about all the replayability I can out of the four campaigns - beaten them all every which way, and am still looking for ways to keep playing this wonderful game!
It struck me that introducing a bit of randomization in the setup could allow for greater replayability.
I'm not talking moving setup locations of units necessarily... but introducing a bit of variation in steps, reinforcements, and attachments could make for some interesting variation. For instance, say each unit has a 5-10% chance of having +1 step, or -1 step. And reinforcements come a turn early (10% chance) or a turn late (10% chance). And air power is varied, say 10% chance of getting +1 or -1 air strikes each turn. And maybe the computer gets 3 extra attachments, which are randomly spread across the forces. Or the players attachments are randomly distributed.
This could also be reflected in different difficulty options - ie, a "hard" difficulty option where the computer mostly benefits from the randomisation, and the player mostly suffers...
I know the scenarios are all finely balanced at the moment, so this option would risk unbalancing things a bit - could make some scenarios impossible, while making others too easy. So of course this would be an option to be checked at the beginning of a campaign, with no pretense that the resulting campaign would be "balanced".
I wouldn't have thought this would be a difficult option to implement, perhaps in a patch?