Official as in approved by ISO, no.

Likely to become official, yes.

BTC is out of the game because non-country codes can only start with an X.

Therefore, currently running candidates are XBT and XBI with rare mentions of others. Before you suggest XBC, it's already taken by European Union (though not in active use any more). Trust me, once you get used to it, XBT sounds quite powerful, definitely more so than XBI.