As of now the only way to get resupplied as a marine is either an armory (which needs to be build first) or direct commander support (which requires the commander to nanny single players/groups and also costs his plasma) while aliens can be entirely self sufficient (regeneration upgrade/no ammo needed). So I had the idea that MACs could, after an upgrade, function as mobile dispensers. Kinda like the ones in Team Fortress but mobile. They generate ammo/health over time and give them to players just like an armory would. No weapons could be purchased tho.
MACs are very vulnerable which is pretty lame considering they cost 5 res. So I propose a turret upgrade which adds a little sentry turret to the MAC that automatically attacks nearby targets. Not a very powerful one but just enough to have a fighting chance against a single skulk.
Same problem again: vulnerability. Something that makes MACs tougher.
Self repair upgrade
I always have the problem, that I need at least two MACs so they can repair each other. Not like a player gets his hands dirty by welding that thing. So I propose a self repair upgrade that lets MACs repair themself over time. Maybe only while idle. Or slow when busy and faster when idle. Something so I don't have to nanny them as well.