The reason why it was announced -formally, let's not forget- by the palace at the event of Charles and Camilla's wedding (which after all was not that long ago) that she would be styled Princess Consort when he becomes king may have been whatever it may have been -a sincere statement or one reasoned as you describe above. The heart of the matter is, it was official -and as official as it could be. Nothing has officially retracted it since. And nothing can do it. If the palace said so -when they had every expectation as you say that Elizabeth will live long-, it stays, whatever the reason for saying it might have been. It's a matter of dignity and decency for them to stick to it. If they don't, it's just going to hurt enormously the monarchy and Charles' reign -alas in a manner that will show in further depth of time. I really hope they don't. And if those who wish the best for Charles' reign want to be of any of use of him, I hope they don't advise him otherwise.
Camilla as Princess Consort will formally be the woman standing next to the King. And she can be as good and helpful consort to him as Albert was to Victoria. It's stupid to risk the seriousness of a whole insitution for something more than that -this is good enough already. For God's sake, people who easily voice opinion otherwise, should simply lend an ear to the arguments of the republicans on the matter...