Hi all just a thought I was thinking this game may be good for a (Decommission Building). So after you have wiped someone of planet you may want to Decommission your army so it is smaller. And collect resources from it to fund else where if you are only army on planet. A simple Building / Factory where all unwanted units can be driven into or land for instant Funds. Simple and quick.
I think you could just do a force reclaim with a group of engineer. With area command it should work nicely.
Good news, you can already do this. It's called reclaiming. It's rarely used for armies (might be viable in PA) but for lower tech factories/pgens it's used quite alot.