These are my first thoughts:
The scenario that interests me is of two great powers on some planet in the far future. They have been fighting a war for a hundred years, both sides are now exhausted and the original cause of the conflict long forgotten. The civilian populations of both sides live mostly underground for safety. For the last decade the military forces of both sides are at a stalemate, having very little left in the way of heavy weapons , tanks and aircraft. They have technology, but no infrastructure or heavy industry to build it. The armies are basically reduced down to a technology level not much better than WWII, with the exception of a few armoured battlesuits, drones and robots used by the elite units.
(This allows me to use or adapt some WWII rules )
Peace would be the obvious option but both sides are committed to wiping the other off the face of the planet.
The surface of the planet is a wasteland, poisoned by nuclear and chemical weapons. In this terrible environment mutants roam, the pitiful twisted remains of both animals and men, soldiers who have stayed too long in the contaminated zone and can no longer be allowed back into civilization.
One side I will call Union , the other Rebels, until I think of something better.
The main military missions of both sides are raids to steal healthy civilian women (for breeding purposes) and take prisoners for Genetic experiments.
The contaminated No-Man's Land has forced both sides to try to find a way to wage war in these conditions.
The Union, which is richer and has more resouces in this area, has created a new breed of genetically engineered soldiers (Genetic Rangers) who are at home in the Wasteland and can operate independently. This has put the Rebels on the defensive.
In an effort to combat this threat The Rebel scientists have implanted robot controllers into the brains of mutants gathered from the wasteland. These are grouped into units under the control of a mutant handler. These units however are only an expedient adhoc solution, as they can be sometimes very effective but other times unstable.
The second solution by the Rebel scientists has been to genetically engineer Union prisoners into fearsome mutants known as Cyclops. These are also under the control of mutant handlers.
The third solution has been to feed and rearm the human mutants of the wasteland into military units with the promise of curing them . These units are of very low quality.
From time to time both sides have employed off-world mercenaries . The mercenary units employed by the Union are well equipped and well disciplined .
In contrast the less well off Rebels can only afford fortune hunters and ex-soldiers from all over the galaxy that vary widely in quality, like the rest of their army.
So much for the war.
The planet itself is quite rich in rare minerals such as lithium. This means to add to all its other problems, it gets raided quite regularly by Space Pirates.
Rules: no idea as yet.
Space Pirates: Chiltern Miniatures and anything that will fit the look.
Union Troops: Ironwind Vor Union infantry
Drones : As above.
Union Genetic Rangers: Ironwind Special Forces, probably painted blue
Union Mercenaries: Pig Iron Heavy Infantry, with some vehicles and aircraft from Old Crow
Rebels: Pig Iron Kolony Militia
Rebel Elite Troops : Ironwind Neo Soviet Vanguard
Contaminated wasteland Militia : mix of Pig Iron Kolony Rebels and Kolony Ferals and Ironwind Neo Soviet Chemgrunts.
Mutant handler and mutants: Ironwind
Cyclops : Ironwind
Rebel Mercenaries: random Warzone miniatures that fit the bill, most I already have.