I was playing a coop mission online and engaging the enemy from 300+ meters because getting any closer meant death no matter what. At this range I was able to take down one enemy before a slew of very accurate bullets came flying at me. I managed to avoid death and ducked down the hill in an attempt to break their view and try another attack. I crawled back to a new firing position and no sooner than the enemy was in view I was engaged again. This time fate was not on my side and I was killed almost instantly despite being in a new position about 50m away and remaining at least 300m for the enemy position.
Despite leaving my old position and low crawling to the new position the now alerted enemy was able to engage and kill me in mere seconds faster than I could aim down my scope.

http://www.youtube.com/watch?v=7XJu-2E7RT4

Navy SEAL's obstacle course. This man easily navigates up a tower about mid way through by jumping and grabbing on the the ledge above him and pulling himself up from there.
In another portion the man jumps up and grabs onto a log, climbs onto the log, and then jumps to another higher log before dropping to the ground. There is also the "Incline Wall" and "Vaults" where the man grabs onto the ledge of the obstacle and jumps over to get over the obstacle. IMO these would be better than the current vault/high-step animation.

Dr Death,
I'm saying that punching is not a viable option in a combat scenario. If you read the rest of my reasoning I go on to give other options of hand to hand fighting. If they are going to go as far as to add something like Krav Maga then they may as well turn it into a fighting game and slap street fighter on the title. Unless they utilize keyboard keys to add other types of hitting the opponent melee would purely be done with a mouse or controller, either of which only have so many buttons to program, thus limiting the number of "moves" the player could do using them. Therefore anything more than punching or kicking would be very hard to accomplish without leaving the mouse or movement keys in order to do. They also cannot make certain "moves" as it would give the player without the gun complete control of the situation. If I were to run at you and do a "move" to knock your gun away and leave you with only your fist to fight as well. You just went from a huge upper hand to having a level playing field all by me doing some sort of melee attack that you may not have had time to do anything about. To make hand-to-hand combat possible it has to be either completely ridiculous or not at all. The idea of the combat knife is the exact same thing. There are only so many buttons that a player can use without leaving their normal WASD keys and mouse. Unless it is a pre-scripted movement you can do, they would basically run around doing a limited number of slash/stab movements hoping to hit an enemy with them. Look at Day-Z's hatchet and crowbar. Both of them are melee weapons that have one range of motion to them achieved by clicking the fire button. Maybe they could add more with different mouse buttons but then they would be relying on the players to have a gaming mouse or at least a mouse with more than the normal three button set up. The only other option is to resort to the key board and again we go back to the fighting game style of combat. Aside from all of the control side of things players don't often come close to other players. The addition of a combat knife or any sort of melee would hardly be used in the fight since most players keep more of a gap between them and their enemies than what could be closed to fight via hand to hand or with some sort of weapon. When using a knife for self defense the general rule is 21 feet. That is 21 feet is the furthest a person can sprint and close a gap to cut their adversary with a knife. 21 feet, or about 7 meters, is much closer than most, if not all, of ArmA's combat takes place.
Dr Death you said in a previous comment that "...in the old ages they used knives and swords to fight..." and you are very correct, however, there is a reason why they stopped doing that. The Samurai were considered some of the most lethal of all of the swordsmen of their time, yet they still fell to the new technology of gunpowder. The bladed weapons were basically useless because their enemies had flintlock rifles and were very capable of taking down the advancing Samurai before they even had a chance to fight back.
To briefly touch on my previous comment where I said punching would be ineffective. We are talking about a combat scenario where the personnel fighting are wearing combat gear, plate carries, and magazines. The idea of a punch, or even a knife stab, to be an effective means of fighting an enemy while both parties are wearing this gear is null. The movement range of the attacker is quite limited. Aside from the limited motion, the punch or stab would not likely be felt through double, or even single, magazine pouches, the ballistics plate, or the stab vest that would likely be under it. Unless the player can also target such attacks on weak or uncovered parts such as the neck, face, arms, or legs, which again goes back to my limited mouse control argument.
To wrap things up a means of melee combat would be ineffective in game such as ArmA due to the limited mouse buttons, the players engagement range, and the gear of the players themselves.

tl;dr combative melee techniques would not be effective in ArmA.

Downvoted. A melee weapon is not exactly realistic to combat. Unless it were hand to hand which would be an unrealistic request as punching would not be effective. Real techniques, such as fighting for a weapon or knocking it away, would only work if they were pre-scripted such as hitting the enter key to grapnel the weapon and fighting the enemy from there. On the combat knife side of things the only way i could see this working is the battlefield 3's combat knife take down. The expression "taking a knife to a gun fight" exists for a reason.

I disagree. Moving and shoving a pistol into a drop leg holster is not an easy task. I assume more so when under fire.

Edit maybe when slowing to a walk while standing, but not when crouched or prone.