I'm kind of hoping Iris will be doing Gym battles since Dento, based on evidence form the games apparently, will be doing Musicals. So... In that case, it would be Ash teaching Iris the ropes of Gyms.
Then, in my head, N will be Ash's main rival, with White as a side rival, and at some point in the League (which, again, in my world, will be filled with good matches. Three six on six battles, please? That Ash wins... Then in the finals, he'll lose against some dude. Maybe Black? Or maybe White... Even if he would only win two six-sixes.) he will have a full battle gainst Iris. It would be good because they'sd know each other's strategies and it would be epic.
Final battle: Kibago final evo vs Mijumaru final evo?