A separate clothing slot is an interesting point.
On one hand, it's the method of picking the "coolest looking" armour, with the stat points of the uglier, bulkier armours (like in an rpg with a female warrior wearing a small necklace to give the same protection as a massive helmet, so she can both 'look sexy' and 'not get killed easily').
On the other hand, it would allow a lot regarding customisation, which is one of the main aims of the 3D work - i.e. a gang may have many different armours amongst their members, but all wear jackets / bandanas / waistcoats of a particular colour to help identify them.
However, I don't know how easily such a thing can be implemented - I don't know if the clothing layer setup was part of the original engine, which we cannot change ourselves, or whether it was something Karpov added himself.