Setting down this road may sound good in light of what we face, but wait until a group makes the same claim about Christians, Jews, or Buddhists. Do we want to start down that slope?
But I agree with you in principle. Such a constitutional amendment would never fly. Not because you are right, but because that's how our constitution is interpreted by those who continually tear it apart, those who would see all religion destroyed in this country, not that it will happen.
Christianity may be all but destroyed, and when a void is created, something inevitably fills it, and Islam is very adapt at doing just that. And as it does, it will press for more and more law to protect it from being attacked, spoken of in a bad way. Slowly but surely you will loose all freedom as you know it, and generations that follow will never have known it.
The Christian freedom this land once knew, that is already badly eroded, won't even be a distant memory, because there will be nobody left alive to remember it.
Of course something is predicted to happen just as the last of Christianity fades from the planet, because the faith that keeps this planet- and whole universe- will no longer hold it together.