As Miranda Priestly ­might say: Florals? For fall? Groundbreaking! Next season’s fashions are ­bursting with heavy petalwork, romantic prints, and artisanal styles. Break out the big ­earrings and the tiaras. (Yes, tiaras.) Did you feel that? The ground beneath us is shifting. It has been for some time, ever since we blurred the noun-verb divide with things like Instagram and Snapchat, and smart-screens stole our gaze. But fall 2016 was the season we realized we were dealing with a tectonic-level transition. Social media has so stoked consumers’ desire for immediacy, were in-season presentations the way to go? Would that be the way to keep the public excited, and to avoid the apparent ennui from the six-month gap between runway hype and store arrival?   The chain reaction began when, days before New York Fashion Week, Burberry declared it would embrace in-season shows in the fa