In my opinion and strictly talking about gameplay, customization goes after difficulty modes. Right now UI is essential, allies have the inverted triangle.
Arma 3 improved a lot from Arma 2, player's movement was one of the most important things, but in some way failed to recreate CQC combat. Your prototype performance is brilliant, smooth as hell, is arma 3 in visuals, but doesn't have the same feeling. I wish you can keep some part of this essence. With minor changes like removing the bullet count from UI you can get back some of Arma sensations.
No offense, but nowadays, Project Argo is in some way likes counter strike more than Arma (I don't know if that is your objective). I played a lot Counter Strike, battlefield, call of duty, but now i'm a bit tired of those kind of games. You have the capability of trying to do some kind of mix, preserving somethings of Arma essence through host options, difficulty/Hud/gamespeed...