I hope we get intermediate scrutiny, but since there are so many gun laws already on the books I wouldn't bet on it. Rational scrutiny, as you stated, allows pretty much anything government does to be valid. As the 2nd RKBA is a newly found right (or we all hope it will be) incorporated onto the states, and the prevelance of restictive gun laws, combined with the fact that SCOTUS is usaully hesitant to overturn vast amounts of laws, I wouldn't bet on getting intermediate scrutiny for 2A laws. Its really up to Kennedy. And it is also likely that the Court will not even address this issue as it is not before the bar in McDonald, so really anything they say in this case (in re; constitutional tests) is likely to be dicta. I'd tend to think they would leave wide latitude to the states on this issue as 7 members of the Court have been appointed by republican presidents who tend to favor those supporting states rights. Here, I can foresee the state's rights issue (and stare decisis) biting us in the @ss.
If Congress were to pass legislation providing for concealed carry nationaly, and do it under the rubric of the Commerce Clause, there would be no way it could fail. (Yes, I know all about the Lopez case failing under the Commerce Clause, however the same law was re-passed by Congress with the words "interstate commerce" included and found valid) Anything that Congress does citing "interstate commerce" gets found constitutional. That would be the way to go to secure the "bear arms" part of the 2nd Amen. I'm not sure if anything Congress has done citing the Commerce Clause has ever been found unconstitutional. I don't agree with this, but that's our history, the 10th Amen. means next to nothing.