From Serebii:
This is really disappointing if true, as it means we'll be locked out from transferring over our favourites for months after release
The Pokémon Company today reuploaded a trailer for Pokémon Bank, but within this trailer's description, it stated the timing for the special update to Pokémon Bank that will add support for Pokémon Sun & Moon, as well as Pokémon Red, Green, Blue & Yellow. This update is currently tentatively schedule for January 2017, later than the autumn timing that was stated in the Pokémon Direct back in February. We'll bring more as it comes so be sure to keep checking back
This is really disappointing if true, as it means we'll be locked out from transferring over our favourites for months after release