Long Nguyen is the co-founder and style director of Flaunt.

PARIS–There hasn’t been a greater moment of anticipation in fashion in recent memory than Raf Simons’s debut showing of haute couture in his new post at Christian Dior.

Since I first saw Mr. Simons’s work in 1996–for his men’s show in the basement off the Place de la Bastille–the Belgian designer’s career trajectory has been fascinating to watch. He made news then with his espousal of youth culture, and he is making news now for revitalizing the Dior house and haute couture.

Taking on and modernizing the heritage of a house with such a varied and deep history isn’t an easy task. Which parts of the heritage should be carried forward? Which should be abandoned?