I've got some ideas on how to do this. Basically make a mod that simulates a Battletech planetary invasion. I'm thinking that some of the ideas used in the Charlemagne scenario for BTS could be employed...
A Battletech scenario would take place on a single planet. There would be one or more Civs already settled on the planet, owning cities and territory. The other Civ(s) would be invading from space, so they wouldn't own anything at the start except some units and maybe a military base or two. All sides would be allocated points to purchase units (infantry, tanks, helicopters, etc as well as Mechs), improvements, cities (if not invading), etc a la Charlegmage.
The time scale would be changed to one turn = one day, to simulate the rapid nature of 31st century warfare.
Because of the altered time scale, founding cities after the initial deployment phase would not be allowed. Population would also grow at a much, much slower rate than normal. Therefore players would have to be careful when assaulting cities to ensure they don't end up with a depopulated ruin that is next to useless.
There would still be research, but the discoveries would be much more tactical - for instance, invading forces need to learn what flora and fauna they can eat on this planet (this discovery would reduce military upkeep), ballistics engineers must learn how to compensate for altered gravity (discovery would slightly increase the combat strength of units employing ballistic weapons, etc).
Also, the units available to settled Civs vs. invading Civs would be different to reflect the idea that the invading Civs probably have control of space, so they can bring in advanced weapons and elite reinforcements from off-world. Settled Civs would likely have to make do with whatever was already on the planet.
The different kinds of weapons on mechs (energy, ballistic, missile) could be simulated with the use of bonuses. Mechs with energy weapons and jumpjets would overheat in desert conditions but perform well in artic or tundra, and also perhaps swamplands (the water would cool mechs down). LRM mechs would perform well in open ground (plains, grassland, desert) but poorly in forests.