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>GB -> GBC transfer possible
>GBC -> GBA transfer impossible
>"M-muh stat changes!"
>GBA -> DS transfer possible
>DS -> 3DS transfer impossible
>"M-muh servers!"
Noticing a pattern here? Every other hardware generation, Game Freak makes up some bullshit excuse to make the older games obsolete. This lets them market remakes of older games to collectors, who are forced to buy the same titles over and over to complete the Pokédex.
There were never any real plans to release the Pokémon Bank internationally. They announced it purely to silence complaints about the lack of transfer features, and gave it to a few players to silence rumours that the app is vaporware.