First off, I am a great fan of this series of games. By far the insurgency series portrays tactical combat at its best in a video game. For the newest installment I have some ideas that could make it even better.
Different animations for ways to grip your weapon.
One of the easiest ways to show whether an individual is highly trained or not with a weapon is their grip. There is a reason operators never hold their carbines by the mag-well and why the C-clamp grip with a stretched forward arm is the preferred by SOF. I won't lie when I say I cringe with the current grip animation for the Mk18. That said, perhaps grips can be another customization option for the player, choosing how their character grips their primary weapon (I.e. Underhand, C-clamp, or mag-well hold) would be a great feature. To make matters more interesting perhaps each could have slightly different traits that affect accuracy, aiming speed, and recoil management, as they do in real life.
Visualize/Customize kit and armor.
It would be a nice touch to be able to enable your character to don his kit while customizing and having him/her keep it on when back to the main menu. It's a small touch but it would improve immersion and better allow us to customize our soldiers. Perhaps some customization on the kit themselves would be a great addition. Different body armor types (JPC, CPC, IOTV, Slick vest w/ FLC or panel), camouflage patterns to match our characters, and accessories (I.e. compass, GPS, chem lights, Flex cuffs, knives, IR strobes, smartphone TAC, admin pouches) as well.
Overhearing real voice communication.
To increase realism, in VS. matches it might be a great feature that if you stand close enough to a enemy player that is using a microphone you can hear them (just like footsteps and character voices). It would add another level of depth in the tactical aspect of the game.
Diversity in insurgent characters.
The insurgent team has a very standard selection compared to security. This could be improved by adding veteran styled options for the insurgents, I.e. foreign fighters and ex-military. For example, a insurgent could style themselves as a Afghan Taliban fighter with tunics, turbans, and coats. Or they could elect for a veteran foreign fighter I.e. Chechen or Russian (introducing new voice option like in the security side).
All in all this is a terrific game, and I look forward to its future developments. An offline mode would also be welcome for us in the line of work that cannot be online for long periods of time.