Pokémon Bank has been re-added to the Japanese eShop for all to download. This has been done with an update for all players who previously downloaded for both Pokémon Bank and Poké Transporter. The patch is said to add countermeasures to prevent the software from causing the servers to overload. The free trial for this software has been extended with it ending on February 21st 2014.
No word on its release elsewhere though, but hopefully this means it is in the near future