Survivors have direction change based slowdown, building momentum in this way should also apply to killers. Killer's drive chases, this shouldn't be a problem. It would also stop the egregious use of massive angle changes on lunges.
Is it an egregious use? Cause I think it seems pretty reasonable considering "aim assist", which we can't turn off entirely, often makes standard attacks smack at non moving terrain objects even though the killer had the survivor centered.
Also killers don't gain speed when they move. They are already at their base top speed at all times. If you want to talk in terms of realism you don't really lose much speed when turning while walking. Killers just power walk everywhere so what speed is their to lose.