"BTC" is not a good or likely
ISO 4217 currency code. There are two kinds: country specific and everything else.
The country specific codes start with the two letter country code followed by another letter, often the first letter in the name of the currency. "USD" for US Dollar and "SEK" for Swedish Krona. "BT" is the country code for Bhutan.
Non country specific codes start with an "X" followed by two letters describing the currency. "XAU" for gold and "XDR" for Special Drawing Rights. The natural ISO 4217 code for Bitcoin would be "XBC". "XBC" is currently taken by the obsolete European Unit of Account 9 so maybe it can be reassigned. Or maybe the ISO 4217 Maintenance Agency can make an exception if "BTC" becomes established enough but it would be kind of ugly.