Okay, now Imma start off by saying I don't expect a Commander Shepard level of customization, but I'd certainly like to have more options.
First of all, I'd like hats, before you say "GO BAKC TO TF2 YUO CASAUL NU0B!!!!!", shut up and listen. I'd also like to customize the shirt, gloves, and pants. And race too, since the US has such diversity, and Russia is adjacent to China and Mongolia.
Now by "customize" I mean swap models and patterns. For example, let's pretend I'm playing as a US Assault on, oh, let's say Sharqi Peninsula. I switch the race to caucasian, give myself rolled up Engie-style sleeves, put on Multicam and I'm done. Now I'd favor doing this in-game, but I'd understand having to go to the menu. Or maybe I feel like making my US Recon look a little different, so I swap my homemade facemask for an Engie-style baseball cap, and change my gloves from the skeleton ones to regular tan Assault ones. Maybe I'll change my boots, gloves, and armor from the default Coyote Brown to an Olive Drab color. Of course, this is for the US side, but the RU side would work the same way.
In a nutshell, it would involve switching between the different apparel the classes wear, and giving (class A) the (apparel B) of (class C). That, and being able to switch the color of boots, armor and gloves between the default colors and two other shades (the available colors being Olive Drab, Coyote Brown, and black).