Clearly that is the direction that this particular brouhaha over the Second is trending and is one reason why some of us are a little concerned about intervention on this issue on the restriction side by the federal government, should that be the way the decision goes. How much latitude the states really have on the matter will almost certainly undergo some change out of this, and call me paranoid if you like, but it seems that gun control advocates would find it much easier to pass one draconian law nationwide than attempt to address the issue in the various states. In fact, they've tried that and with the AWB succeeded, at least partially.
Still, it would be interesting to get a definitive view, however narrow. The entire body of gun control law isn't likely to shatter because of it, however much I'd prefer that personally.
The Supremacy Clause of the U.S. Constitution says that federal law supercedes conflicting state law. In addition, most rights contained in the Bill of Rights, protected under the U.S. Constitution, may not be infringed by the states. It didn't use to be that way, but it is now.
Voting laws were, and are, left up to each state. The federal government has no power over those laws. If the states required a literacy test or a poll tax, if they excluded non-whites, women, those under 21, etc., they were free to do so. Amendments to the U.S. Constitution changed that, and the 14th amendment made those rights applicable to the states.
The second amendment has not yet been "incorporated" and made applicable to the states (neither has the third amendment, the grand jury indictment clause of the fifth amendment, and the seventh amendment).
Therefore, the second amendment only applies to gun laws written by the federal government, not the states. In other words, the federal government may not violate the second amendment. States can.
If the U.S. Supreme Court reviews Parker and decides that the second amendment does not protect an individual right, only the residents of Washington D.C. are affected -- the federal law only covers the residents of Washington, D.C. No state laws would be affected by this decision (since, again, the second amendment doesn't apply to state law).
What would happen is that state legislatures would look at the U.S. Supreme Court decision and use that as leverage to pass more restrictive state laws. Of course there's no connection, but liberal legislators will make one.
Now, states may always write laws that are more protective of rights than the federal government. Unless, of course, those rights conflict with rights held by others.