IIRC while stargfing in RO you have already speed penalty. Only possible thing to make it less-usable would be to decrease accuracy while strafing.
Problems are, that 1. everyone is an invidual. Some people might be able to sidestep without any problems while some are clumsy and cannot perform that. Even with all gear added you would carry during the second world war (or with modern armies, similiar idea still), some might still be able to do that, while some instantly fails.
This leads to a problem that we need like 1000 random profiles that are given to each one that varies their psychical ability. Of course, the biggest problem of this issue is that we would need more realistic stamina system, which IS impossible to implement the proper way. You need to take so damm much crap into account that 90% servers would be overloaded already by the fact the game needs to calculate too much crap. Also add some firefights and voilah, servers are turned into coffeymaking machines or eggcookers. Varying stamina might be suitable, but that's still far from realistic and I can imagine the amount of whining it might cause.
And now this leads the problem that RO is just a game. Yes, this is retarded and overrated argument, but it is just sad fact. Sure we want to improve the realism, but it is ironic that more realism -> more balance. Sure some people might say "screw the balance", but I doubt that might do any good. Sure the hardcore armchairrealismgenerals might be happy, but what about those who draw logical line between gameplay and realism?
Oh... _those_. Screw them! Realism ftw! Super hard-core analic authenticity ftw also!
Really, no matter how much we discuss this we are handicapped by some major facts. I don't mind improvements, but be realistic. Strafing is there for the fact that you can't properly implement basic body-head functions in a simple FPS game, unless if you want to make similiar system as in OFP, that you need to use keypad to turn your head around while not moving your body. Oh sorry, I forgot if you do that you need to let go of your mouse for a second. How unrealistic it seems that with that your reflexes are way worse than they might be.