On April 15, Muriel Bowser, Mayor of Washington, D.C., said she will ask the city council to put a ballot measure on the November 8, 2016 ballot, asking if D.C. voters want D.C. to become a state. See this story.
The referendum might be more interesting and useful if it also asked residents about the option of ceding most of D.C. back to Maryland. When Puerto Rico has had popular votes on its future political status, the voters were given several options.