In no way does the Heller decision imply that ccw laws are a part of the 2nd Amendment. They (the High Court) were pretty specific about that in their opinion. Nor did they put the 2nd into the status of "incorporation" which would force the states and local jurisdictions to recognize the federal mandates.
Any EO has to be published into the Federal Register for 90 days before it becomes law. Any state can oppose it during this time via the Senators or Congressional representatives. There have been EO's halted this way in the past, most notably during the Clinton regime.
I very much doubt that "O" is going to be successful in issuing such a restrictive order in a non-emergency situation. But therein lies his secret to a successful coup. All he needs is a huge emergency like a terrorist attack or a huge natural disaster like a tsunami that struck multiple states along the eastern seaboard. Possibly an economic meltdown that saw rioting in multiple states.... Come to think of it, I've suddenly seen DIRE warnings of just exactly this scenario taking place..... Think his minions in the media are greasing the way by prepping the populace for draconian solutions?