That is an interesting suggestion, and I'm going to try it, but don't you think that kind of defeats the purpose of the scope? I mean, if I'm going to go to the trouble of sighting all my targets with ironsights, why waste precious time going back to the scope when I can already hit the guy? We've seen 200+m kills with un-scoped kars and mosins, so having to switch back and forth to make kills is a bit of a hassle, especially once you get to a point where you can just grab the SVT.
Most of the marksman rifles technically have iron sights, but try it out and you'll see that is not a terrific idea. It is usually looking through a lot of metal and woodwork, then having a tiny slit in the middle where the iron sights are. Can't see much. Much, much harder to see or aim at stuff with that compared to the standard rifles without scopes. And yeah, within 150 meters scopes are usually no better (or worse) than plain iron sight rifles. It is annoying to have a marksman rifle then finding oneself using the gimped iron sights to shoot with, realizing it is better than the scope.
Only go marksman when the map has long enough distances and hiding spots to warrant it. Otherwise, do your sniping as a rifleman. Can see, shoot and hide just as well in most situations.
EDIT: switching between iron sights and scope can be done instantly if you bind the "weapon function key" to, for example, a mouse button. I have it when tilting the scroll wheel right.