Right now it is hard to say. We have to see how easy QSing ends up being in this game. You need to remember something, the core version of this game is going to be playing slightly different then MW2. With all guns basically being given stopping power now, the QSr who misses their first shot or is not quick enough won't stand a chance, even against the most basic of sprayers. Remember, QSing works on all weapons. One quick pull of the trigger when an opponent is somewhere near your sights and you have them. In MW2 a lot of the victims of QSrs were those that were running non stopping power classes (ghost, dc, hard line).
This is just what I suspect we will all be hearing from vocal minority known as QSrs.