TheCityFix thinks the switch makes sense.
"[B]ecoming a city would be self-reinforcing in terms of making good transportation decisions. I think it's safe to say that at each moment in the foreseeable future, the City of Fairfax (the new one-it'll be fun to watch them negotiate a name!) will make better decisions on transportation than the VDOT. As you get more transit users, more pedestrians and more cyclists, you will get more local demand for that kind of infrastructure, and the divide between Fairfax policy and VDOT policy will only widen."