In recent weeks, the idea of closing Rikers Island, the sprawling jail complex in the middle of the East River, has once again become a central topic of public discourse, with both Gov. Andrew M. Cuomo and the Council speaker, Melissa Mark-Viverito, arguing that it is the surest way to put an end to the brutality and dysfunction inside city jails. Supporters of the plan envision whittling down the city’s inmate population, already at historical lows, and then dispersing the inmates still incarcerated, including those charged with the most serious crimes, to a constellation of modern neighborhood jails in easy proximity to families, lawyers and courthouses. But can it actually be done this time? Skeptics, including Mayor Bill de Blasio, argue that while the idea is a noble one, in practice it is highly unlikely to be realized: to succeed would require years if not decades, billions of dollars and enormous political capital, while distracting from efforts to address immediate problems facing the jails.