Just like the tabletop, all they need to do is assign point values to various item drops, allow units to level up, be traded, maybe even die or lose xp somehow. Point is, you'd simply create your own squad with your point limit, which rises and gains access to better soldiers and better gear as you level, and you travel around with this squad. At first you may only have yourself, the hero. Then you get a guy or two, equip them with basic pistols. By the end, you're sporting a unit of 10-20 troops, featuring elite types, anti-tank weapons, and flyers/bikes. Hell, maybe the top tier players will even be Daemon Princes or have access to titans. How cool would it be to see an Avatar fight a Bloodthirster?
