For gaming a character, two things need to be separated:
* The visual sway, acting as an indicator for the amount of sway you suffer from.
* The actual sway, forcing a bullet spread, to avoid solving it with "good timing".
If I were designing the system (for realism), I would use breath holding to reduce sway by percentage and fixed. So even a super experienced sniper would have to hold breath for maximum performance. Then consider factors for weapon length (would also affect inertia, but hard to "get right" in a game, although ArmA has it in some modes), weight, character strength, stance, weapons mods and rest, and finally skill. Having skill at 20% increments wouldn't be that bad if its impact factor was affected by many other factors. As a weakling, I would suffer horrible sway trying to dual wield a couple of M82's in a running fashion.
I would even consider two separate sway axis. Up/down for normal sway governed by mentioned factors, and erratic sideways sway if exhausted after sprinting (holding breath factor time/factor would be like 10% of its maximum capacity).
All that said, calling FO/FONV "sniping" is a joke considering the tiny distances. Considering being RPG a lot of factors could be taken into account, but I wouldn't go as extreme as Arma/ACE3 stuff. All we need now is velocity sensitive mouse buttons to measure and compensate for trigger discipline 
As for what will actually happen, I guess we'll have to see. I personally don't expect it to score very high in the realism area, as older tabletop RPG games might do (never dealt with bullets though, but fairly complex rules for everything nonetheless).