Something else found on the French forum about the same question. Thx to masahiro for this.
It have been post in september,

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Hello!

Currently plans for the future of the server have not yet been finalized. Same thing with regard to the modalities of transfer at the launch for A Realm Reborn.

We expect the beta to determine if many players will return to the game (former players, who already have a character assigned to an existing World). Future decisions will be made ​​based on these figures. It is possible that the Ten Worlds today are no longer sufficient to accommodate all the players, which will influence our future decisions.

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