Pokemon Bank (and the Pokemon Transfer app that allows players to transfer Pokemon from Generation V games into Pokemon X and Y) was supposed to be released last year, but server issues with the Japanese version of the application caused Nintendo to pull it from the eShop, as well as delay the release of the North American and European versions of Pokemon Bank. Little has been heard about the application since then, but as of today Pokemon Bank as again launched in some Asian countries.
Nintendo of America has also spoken up about Pokemon Bank on Twitter, basically saying to keep an eye out for more infomation on a future North American release. Nintendo of Europe has said much of the same on the manner, stating that they are observing player experiences and any issues while preparing for the European release.
Still is still no solid release for Pokemon Bank, but should the Asian versions remain stable, we should be seeing the application coming worldwide soon.