The situation was somewhat different, though. Mette-Marit wasn't in the position of being perceived to have been instrumental in breaking up a previous marriage of Prince Haakon, and she wasn't replacing anyone else as his Crown Princess. The situation is somewhat more similar to that of Liliane Baels having to settle for a lesser title as an unpopular second wife of King Leopold, and she didn't even have anything to do with the end of his first marriage.
At the time when the engagement of Charles and Camilla was announced, I'm not sure how well received it would have been if it had been stated that while Camilla would be known as Duchess of Cornwall for the time being, she would be Queen Consort to Charles when he became King. It would have been the courageous thing to do (always assuming that the "Princess Consort" thing wasn't Camilla's idea and the condition upon which she agreed to marry Charles), but it might have had dangerous consequences at the time, when so many people still had raw nerve endings about it.