Costume historians will doubtless look back on the day Karl Lagerfeld died in February 2019, leaving in his will lavish instructions for the ongoing care of his Birman cat Choupette, as the precise moment when the fun finally went out of high fashion. Yes, it’s possible another full-blown eccentric will one day preside over a big house. But it doesn’t feel, in the era of the global conglomerate, terribly likely. “Creation,” as Lagerfeld once put it, “is not a democratic process.” The more people (I may mean accountants) who stick their oar in, the more likely we are to get...