First: Create a Hard Core mode, even if that's just a test to see how the community likes it
In hard core mode, every bullet counts more, players either die with one only shot, or if the shot hit the armor the player will fall to the ground but not die. Anyway, no one will be able to immediately return fire when take hit. This would bring back the old Insurgency games feeling where weapons feels more powerful and deadly. I really think that Insurgency players are the players looking for a more hardcore and realistic experience in the game world.
Second: Add a "one button lean control" (Player will have Q and E key free for use in other shortcuts)
For example: If I use control key to lean, when I keep Ctrl pressed and hit D, the character will lean right, and if I keep D pressed it will walk right while leaning. When I release Ctrl or press A once, the character return to normal stand position. So Cntrl plus A or D would be a good new way to manage leaning mechanics. (I am not saying to remove the current lean system, I'm just saying to add more options).
Third: Add more difficulty levels to Local Play.
I saw people complaining that local play was too hard long time ago but now is too ease in a sense players can let go tactical play and just run and shoot. Devs could just make current difficulty setting to be the normal setting and the original, used in the early days of the game, to be the "hardcore".