With usf we really should look for things the ardennes assault has. Like the hunker down ability, cache supply points, man the defenses and (i have repeated this one too much like a parrot) rifle satchel charges.
Maybe you could also look at axis abilities that fit to the theme of Urban Assault:
3CP - Infiltration Tactics come to mind, would give US access to grenades to clear houses without the need to tech for it. Sector Assault from OKW's Breakthrough could also be interesting (reworked of course) because of the mix of shells and smoke.
About Soviet Airborne:
An Air Assault Engineer unit is not used by other factions although these units were always part of the first wave. Could be an interesting alternative. Air Assault Guard Engineers could be the only airborne unit with access to flamethrower then.