Personally, I wouldn't mind such a thing. As ghamorra mentioned, it's pretty silly for SMGs to be able to hit almost as well as ARs and LMGs while only needing to take 1-2 more rounds which is more than made up for by their rate of fire.
As a whole though, I just know that if such a thing were implemented, there would be non-stop crying by spoiled players.
Such trajectory stuff would also help mitigate complaints about use of the Thermal Scope and Tracker Sight too. As I keep saying (and have said with the Target Finder in BO2), their purpose is to help find targets. The actual aiming and firing is still entirely up to the user which is why people who try to complain that "only people who can't aim use it" as their argument against such things are only hurting their own side since they're really saying that they're constantly getting killed by people who "can't aim", period.
Been discussed for years. What makes COD is the reason it IS COD and not BF.