very cool. I like those!
just for the record: is it easily possible to have inventory screens with only some of the inventory slots?
it wouldn't really make sense to have a backpack for most of the aliens, since they don't appear to wear real armor (most are naturally armored or have armor grafted onto their bodies). I guess the only alien that should have a backpack is the ethereal. who knows how much stuff they can hide under those cloaks?
come to think of it, perhaps the flying armor should use all or most of the backpack slots for the "engine"? you might even think about making the "flying engine" an equippable item instead of a completely different armor.
also, some (e.g. terrorist) units shouldn't be able to carry weapons at all, so those slots should be disabled or hidden, right? I guess they are still able to look at items on the ground, though, so that should at least be shown.
which poses another interesting question that has been mentioned before: if we allow large units to see items on the ground (and why shouldn't we? someday a modder might come up with an intelligent, weapon-wielding large unit that should be capable of picking up stuff!), how do we deal with that? will the unit be able to see items on the ground for all four tiles? if it drops something, where will it show up?