I actually love Sara Buys gown! The skirt was surprising and fun, yet the entire look was most elegant. And the tailoring fantastic! I noted that the strapless top was impeccably cut and properly fitted to her. One of the reasons I dislike strapless gowns is that they are seldom cut properly for the individual; e.g., the top is too high or too low or too wide or the little tufts of fat under the arms are emphasized. I noted that, during last week's Academy Awards, some of the strapless tops were just WRONG and had some of the problems listed above! Hard to understand unless the offending gowns were loaners...
At any rate, if Sarah Burton has the commission, her impeccable tailoring will win the day, and the fabrics will be incredible. It surely will not have a fishtail hem, though Kate would look lovely in one, but IMHO, such a gown would be lost in the grandeur of the Abbey. I am certainly enjoying all the speculation!