We can make units, just not 3D models (yet).
I currently have the Cobra Gunship as the American UU, being the principal attack helicopter for many decades (modern black hawks are more of a utility role in troop transport and assault):
24 str
5 movement points
1 first strike
25% Withdraw chance
March
Of course, a Huey or Black Hawk would also be an interesting UU, being capable of rapid troop transport. hmm...
Cobras and Hueys were the attack and utility helicopters (respectively) from about the 50's through the 70's, replaced by the Apache and Black Hawk. The current "gunship" in the game is in the early modern era (being less useful against mech infantry or modern armor), so Cobras and Hueys seem appropriate. I wonder...if you give the Gunship the capability to carry non-Armor units, it could be used to drop marines deep in enemy territory. Might be a bit overpowering though.