The opening and promotional material all indicate that the arc will culminate in the White Ruins, where Ghetsis will control Reshiram (most likely through Corless' device) and use it against Ash and N. The opening also implies that Charizard will make its grand entrance in the White Ruins and save the day.
But then, Charizard is also confirmed to have a role in Movie 16, so it will have appeared in the anime by July. There are two possibilities:
(1) The opening is misleading: Ash and Charizard will be reunited before the Reshiram battle.
(2) The opening doesn't cover the whole saga. The White Ruins will be wrapped up by July, meaning that the remaining two months (at least) of Best Wishes will revolve around something else.
I guess that the former possibility seems more feasible since the openings have been misleading before, but this still warrants discussion.