I just gave a quick try to the Pokebank (available now for my Japanese 3DS) and it's quite well made.
You have to download 2 software, Pokebank and Pokemover. Pokemover immediately detects your 1 box when Black/White/B2/W2 are inserted and asks you to transfer the whole box onto the server (looks like it only accepts the 1st box)
When your Pokemons are on the server, you have the swap BW to insert XY, open the Pokebank itself and you can transfer the pokemons you've just moved in your XY boxes right away. On the same interface, you can easily transfer your XY pokemon onto the server.
I used my French version of Black 2 and my Japanese version of Y, and it worked smoothly without any conflict of region. Kudos to Nintendo for this perfect service (free for 30 days, which will allow to transfer everything I need from B/B2)
