Not a lawyer (but I watched one on TV)... it seems to me that hammering out things case by case on the basis of Due Process or P and I, as deemed appropriate by legal staffers may be the only way we will ever define what A2 means in the modern day.
This issue is that with McDonald we have LOST the chance at P and I and are now stuck with Due Process. If McDonald had been incorporated through P and I, then the only thing left for litigation would have been prohibitions that are currently in place. Through Due Process, not only are current infringements subject to litigation, but any infringements that any federal, state, or local government body decides to implement later are also subject to determination by the Supreme Court as to whether it is "reasonable", "rational", "longstanding", or "essential" to furthering the goals of the government.
Right now I am more worried about having a SCOTUS that votes a split over A2 issues as often as they do.
It is not just that they split on the Second Amendment, it is that we only have one Justice (Clarence Thomas) who sees that government has overstepped the bounds laid out in the Constitution and believes that the rulings which have allowed it to do so should be revisited. The other eight believe that taking any power away from government that the Court has previously granted is wrong.