If the information that the Duke and Duchess of Cambridge will attend the State banquet of the Chinese State visit is confirmed, that will be great news! They have never attended a State banquet so far, so that will be a first for them. Besides, I think it is high time that William and Catherine get more actively involved in royal ceremonial duties. I understand their wish to enjoy some privacy, but I sometimes feel that they show too much distance from royal duties, with quite few engagements, as compared to the Queen, the Prince of Wales, the Duchess of Cornwall, the Earl and Countess of Wessex or the Princess Royal (just my opinion from the other side of the Channel...).
Regarding the tiaras, it seems that royal jewels are now loaned (rather than given) by the Queen to her family(-in-law), and that she loans "only" a few jewels, and not a large amount. Therefore I am not sure that all the tiaras selected by Nellie are actually available to Catherine. And for the same reason, I tend to think that we will see Catherine with the Papyrus Tiara, that we have already seen on her.
I have a soft spot for the Teck crescent tiara, whose delicate design I find really lovely, but according to Hugh Roberts (The Queen's Diamonds, page 122), it has been loaned by the Queen to the Duchess of Cornwall, so it is highly unprobable that it is soon worn by the Duchess of Cambridge.
Roberts also mentions that the Cartier Halo tiara was "loaned [to Catherine] for her marriage to Prince William of Wales in Westminster Abbey on 29 April [2011]", which may imply that the loan was for the specific occasion of the wedding, and possibly not a permanent loan. Personally, I am not a great fan of this tiara on Kate, I think its design better suits a head with shorter hair.
The Strathmore Floral Tiara would be lovely on Kate, and it would be great to see it again, since it has not been worn publicly since the early 1930s...
The Cambridge Lovers Knot Tiara would be lovely, but considering the close association of this tiara with the late Diana, Princess of Wales, I am not sure that it will/could be Catherine's choice (though I would be very happy to see this tiara worn again, because it is really beautiful). Besides, Catherine has already one pearl and diamond tiara, with the Papyrus tiara. NB: the following picture (found on Pinterest) is obviously photoshopped, but it gives a good idea of how this tiara could look on Catherine:
Or, who knows, maybe Catherine will surprise us with a new tiara - why not the lovely Oriental Ruby Tiara, which would make a nice match with her personal ruby and diamond necklace, or with the Greville ruby necklace (which has not been worn by the Queen since the early 1980s):