Skydragon said:Technically Camilla is the Princess of Wales, so I don't really understand the question.
If after the coronation, Charles makes William the Prince of Wales, William's wife (as Princess of Wales) would not take precedence over Camilla, as the Queen consort.
You also asked about the difference between Wallis and Camilla, from what I have read in history books over the years, 2 of the problems not already mentioned here were that Wallis was:-
1. Twice divorced
2. She was an American.
According to my grand-mother, these things really mattered way back when.
Camilla is legally Princess of Wales, but styled as Duchess of Cornwall. Her official precedence in the UK is second after the Queen, but fourth in family terms because she has chosen to assume a lesser rank than Princess of Wales.
Once Charles becomes King, regardless of whether Camilla becomes Queen or Princess Consort, she would be the first lady in the land as the wife of the King. Her title or style has no bearing on her precedence once Charles is Sovereign.
With regard to Wallis Simpson, there wasn't any particular objection to her being American, although it probably would not have been a first choice among the British people. The main problem was she was very recently divorced under highly questionable circumstances and had already divorced once before that. Given the ban on divorce in the Church of England at the time, the King could not possibly marry a divorcee without a conflict in principle.