The concept of 'remittance' tax has been in the new several times over the last several years. It is also an easy tax to implement - Any financial institution simply applies it during a conversion, a defacto collection. Interestingly enough it was just over a year or so ago that the exchange houses began requiring passport/ID info for exchanges.
I would also guess that in the case of a remittance tax it will implemented with no notice to avoid large transfers that would occur if people knew it was coming.