Everything is pretty much leading toward direction of filler saga being made, after Unova league. Games usually come out during september and since it was announced league will be by end of this year, writers will have to fill up time with something before new games come out.
I presume filler arc after league will be dedicated toward new challenge Ash will try to pursue like he did in OI and Battle Frontier, Iris will continue to advance her goal of dragon master especially if she doesn't fulfill Drayden expectations continuing journey to train. While with Cilan there will hopefully be done more about his connoisseur career.
However i think whatever happens after league it will still be treated as part of BW2 season with sequel of BW games not being promoted much at all.
After league, things can go in two possible directions.
Either writers continue with promotion of BW2 games expanding on World tournament concept from games, not staying just on Junior Cup. Which would make sense, because whole Cynthia exhibition match and structure of tournament seemed like prequel to other more sophisticated cups later on which could form Battle Frontier type of quest, after Unova league. Such as Senior and Champion Cup, tournaments focusing on certain type like water, grass, fire tournaments etc. Which would be pretty cool and innovative.
And this could open gates toward return of pother previous traveling companions like Brock, Misty etc being after all in games, and for advance of their stories.
Alternative is doing completely anime exclusive arc similar to Orange Islands, but since writers didn't done that since 1999. and anime today follows games much more closely odds are that first option has higher chance of happening.
p.s.Still kinda ironic to call shorter sagas filler arcs, when OI and BF had a lot of character development and introduced things from games(later one anyway).