Marvel’s turning over a new leaf, so to speak, as it enters the Marvel NOW! era. But in that amid the flurry of new titles, new line-ups and new creators, we’re finding some notable absences — notable to us at least. While some missed heroes like Luke Cage, Iron Fist and Mockingbird have popped up in cameos here and there, there are still a significant number of popular players waiting to be brought onto the field. In this installment of “Six by 6,” we suss out six such characters and zero in on their last whereabouts, and where some of them might show up next.