Unfortunately I don't have my original write up with me, so this is going to be a bit off the top of my head.
Recently I'd been fiddling with GalCiv II, screwing around in the race files and such, when I rather unexpectedly had an idea for a somewhat serious overhaul in regards to Planetary Assaults. Most of the game benefits from it's slightly abstracted nature, but for a while I've felt that Invasions are a bit... too abstract.
Effectively, the idle thought translated to a plan for an interface modification allowing one to equip and train soldiers/build vehicles, replacing the immediate population cost currently in place with an up front fee and maintenance costs. Instead of loading Billions of startled civilians onto a troop transport, you'd have a few hundred thousand military professionals filing on board and such; said professionals would subdue, conquer, instead of annihilate.
Some of this seems possible to me, but would require some rather severe changes to how things are currently handled - the interface modifications I know are possible, changing the functionality of transports seems like it might be feasible, but the troopers, tanks, jet aircraft, etc. would likely require entirely new (or at least borrowed) systems in order to function.
What say ye?