No premiere date was given, but Netflix head Ted Sarandos indicated that the release would depend upon The Defenders, which has a contractual start date after both Luke Cage and Iron Fist debut.
Netflix already has both the second season of Daredevil locked in for this March and the debut set of episodes for Luke Cage later this year. Perhaps they could squeeze in another round of Jessica Jones in the Fall if Luke Cage debuts earlier, but most likely we’ll be looking at a 2017 premiere along with Iron Fist.
But who knows? Maybe we’ll see a new Marvel-Netflix season every quarter.