I know there was talk about it, but I don't know if they actually tested it. MMGs are just pain. Nobody likes dying to them because it's extremely easy to get kills with them. Like the worst player in the world can do well with a MMG if they are defending. You can get a ton of kills with minimum effort. When you get killed by one you're not like "Oh, that was a good shot man." It's more like, "Oh, this prone fuck in the corner." It pisses players off more than recon. At least recon actually has to aim and use skill to get their kills. MMGs is just spray and watch the kills mount up.
-Fix visibility
-Disable the bipod when on your back.
-Give LMGs and MMGs a movement penalty (movement speed and make it so they go prone slower, so they can't dolphin dive).
-Reduce accuracy while moving.