Currently, I feel the MG's have no distinct role in this game, other than it being a rifle with a larger ammo capacity . The real MGs are heavy, but accurate, high rate of fire beasts, which are difficult to use without being set up on a bipod. To balance this out, many games has opted to make them have either bad accuracy, high recoil, or less damage, which are all not at all true to the real life counter parts. If this game wants to portray itself as a somewhat "authentic" (since no game ever is) experience I think it is worth while to balance things the way they should be. I think the game already has all the mechanics to balance them out as well as giving the MGs a proper distinct role, which is different from a rifleman with more ammo. My suggestions are as follows:
increase aim-down-sights time: currently, you can ADS at an instant with an MG. But these things are heavy hunk of metal, most of the weight held with your left hand alone. This will ensure the MGs are difficult to run and gun with.
increase weapon sway, especially if you are holding it for a long time, or out of breath from running. This is just common sense. You can't hold that thing with your one hand for very long, it will get shaky. In fact, even a light rifle is difficult to hold steady for more than a few seconds.
increase cartridge count from 1 basic +1 for each ammo vest level to 2 basic with +1 or +2 for ammo vest level. This will make sure that you can actually suppress the enemy with sufficient fire. However, since there is no over heating or "change barrel" mechanic in insurgency, which is why most MG users don't constantly spray fire, I guess the accuracy of the weapon can decrease due to prolonged fire to balance things out. (Or I guess NWI can add a feature for over heating MGs)
Also, if there are more ammo carried, make them slower, so that they are not running around like sonic and encourage them to place their weapons properly.
I'd say reduce recoil, but from this beta branch, it doesn't seem to have crazy recoil like the last one. However, I still would prefer it to have a little less recoil and more weapon sway for these weapon if possible. As they are bigger guns firing intermediate rounds, meaning less recoil, but difficult to hold meaning more weapon swaying.
Edit: now that I've just played with it, I think the bipoded recoil is still ridiculous for both MGs, and the PKG just has terrible recoil in general. I wouldn't say to reduce too much of it, but reduce it enough to be noticeable. And for bipod recoil, it needs "quite a lot" of reducing.
These will ensure that the MGs has a distinct role and place within the game, rather than it being another run and gun riflemen.
TD;LR, make more penalties for run and gun play, give more incentive for stationary play and increase role as suppression.
P.S. more weapon variety for MG primaries are desperately needed. Perhaps RPK for insurgents and M60 for security?