I am not saying ROHOS has to have anything like their system, or any at all for that matter, but I think something would be nice to at least encourage people to keep their heads down once in awhile.
Probably the most fundamental reason why suppression rarely - if ever (even in DH, to some degree) - works properly is that even if you add artificial ways to enforce the fact bullets are supposed to be dangerous, the reasons why it's bit silly is the fact you can effectively return fire even when you're blinded if you can just remember the rough location of the muzzleflash combined with the fact you can position yourself in such way that would be realistically either truly painful or impossible to fit.
Let's count some examples:
1. Popping up. Yes, you can pop up with a weapon and fire a shot back to very close range at a short notice but accurate fire to a machinegun just by popping up and down is not really feasible. Especially if you're tired.
2. Laying down where you wouldn't be able. Let's say a corner of a building against a tank that you might be able pass while standing, but you would be unable to fit while crawling, atleast if you want to turn more than 15 degrees. Oh and let's not forget shooting while leaning to your left (presuming the person is right handed) - unless you're not ambidextrious by nature or trained yourself to work like that with certain objects, the position you're trying to tilt yourself with a weapon is like pulling your own teeth out when it comes to being uncomfortable. Even with let's say to your right you still would have to put your weapon past the corner first. Clipping is partly related to this issue.
3. Ability to retain perfect aim under any conditions. Even if you're tired as hell you can shoot perfectly accurate shots in RO with rifles if you just do it quickly enough. It doesn't matter if you can't see the target properly as long as you have rough location, as if you got lucky you still killed someone just by aiming for a split second and firing perfectly accurate shot... after sprinting entire marathon under artillery barrage.
DH suppression system (which for the record works ok, but as noted it doesn't solve the fundamental issues) makes it more difficult to return fire, but does not deny it in any real way. Just because you're partitially blind\can't see it properly doesn't mean you can't hit it or aim accurately. Especially with deflection shots.
Operation Flashpoint is probably the only game where I have genuine 'fear' of bullets in pragmatic context that if I am under fire I actually try to avoid staying in the open or seek cover and stay there and re-evaulate the situation. While it's partly due the game being somewhat clunky, it actually effectively denies any attempts to return fire and pop up at will. Double this for FDF mod.