I understand that you think it is an "optimistic move", but I do not think that the Queen will see it that way. (The more that I see of Sister Morphine's postings, the more I agree with her.)
Sister Morphine is taking the historically accurate approach to the question. She's researched the facts. If 29 women married a British prince since the widespread adoption of the title with the House of Hanover (and none were made into princess in her own right) then why should Catherine be different? The 30th marriage was that of Wallis Simpson who should technically have been a princess, but was never referred to as such.
I am trying to hypothesize how the attitude toward titles is changing
1) In 1972 the 26 year old Birgitte Eva van Deurs marries Prince Richard, the
first British Prince in history to marry that is not also a Duke. He is beginning his career as an architect and she works as well. Their plans for a private life are changed as his brother dies 6 weeks later, and his father only 2 years after that. The Duke of Windsor died just weeks before his marriage. With these three deaths Richard unexpectedly goes from a relatively minor Prince to becoming the most senior exclusively-male-line male in the House of Windsor, and the Duke of Gloucester. His career ends as prepare for a life of royal duties.
2) In 1973 Princess Anne marries and refuses her mother's offer for a title for her husband knowing that her children will have no title.
3) In 1974 the newly widowed Duchess of Gloucester dislikes her new style as "Dowager Duchess of Gloucester" and asks to violate tradition and be styled "Princess Alice". The Queen grants permission, even though there is already another "Princess Alice" who is of royal blood. The queen does not issue letters patent.
4) In 1978 Prince Michael becomes the
second British Prince in history to marry that is not a Duke. His wife retains the style of Princess Michael
5) In 1999 Prince Edward becomes the
third British Prince in history to marry that is not a Duke. The Queen takes the unique stance of making him an Earl, and the queen requesting that her successor make him a Duke after the death of both of his parents.
So now history tells us that Prince William will be made a Duke the day before his marriage, and Catherine will become a Duchess. But in the queen's entire reign only a single dukedome has been created (for Prince Andrew), and only 8 Dukes are created in the history of the UK.
Of the following choices:
(A) Make William a Duke of
whatever, which will vanish in importance when he becomes Duke of Cornwall but will be carried down his male line for possibly hundreds of years. Yet the only real reason for this title is so that Catherine will have a non-male centered style,
(B) Have Catherine adopt the title of
HRH Prince William until Queen Elizabeth II and Prince Charles die,
(C) Make Catherine a princess in her own right.
I think that choice (C) is more consistent with the changing attitudes, and the desire not to create new Dukedoms for Richard, Michael, and Edward.