As long as it tops the 3 million mark like WANEGBT who cares about longevity. WANEGBT had more impact as a break up anthem than some of the songs that stayed at the top for more weeks or charted longer. We know her sinjel sells are front-loaded. What matter is the total sells when all is said and done.
Note that Brian Mansfield is the journalist who after previous interviews with Taylor revealed that TSOU was also about John Mayer and also that IKYWT and Treacherous were both about the same person (ie Jake Gyllenhal as revealed in The Temper Trap connection).
I am hoping that he will interview Taylor for LP5 as he usually has a scoop about the original muses of the album tracks.