As confirmed today, we now know Iris will be a Gym leader after BW ends. Unlike the last minute decision for Misty, it seems Iris planned to be a Gym leader right from the beginning.
With Cilan however, they aren't setting up any reason for him to depart. Its almost like they're treated him like Brock, where his goal is so open-ended that he has no reason to leave Ash's side for the time being.
It'll be very interesting to see what happens to Cilan after the league IMO.