As some one says: want it = make it.
So my suggestion - make for German and MEC forces MG3 to replace HMGs on them.
General reasons:
For German army:
1)They don't have M2 .50cal MGs in real life.
2)They got too much heavy armored vehicles(IFV Puma also called Infantry Tank in German language (Schutzenpanzer))
3)Make less asymmetry on Silent Eagle.How this is to much asymmetrical balance cuz every german vehicle have thermal sights and big armor.Rus side no have thermal sights(On APCs) and have paper armor(But have overpowered 30mm cannons and Tank Guided Missiles

For MEC:
1)They could be have BMP2M.they could be muck overpowered that BMP3.MEC team must be have some bad sides.
P.S on Kashan G3's recoil isn't bad side - they got more power thats M4.
This Tripod already got scope what make this better thats other HMGs.
In my opinion - madness firerate make don't make this MG less powered against infantry targets.
So there is pictures(MG42 mounted,but tripod must be right):



And I think ISAF must be have leet mount with EO-Tech reflex sight like this IMO:

And what I make(not so much but am just started.)

