+1 for this topic
I don't think it is correct to (ab)use the Bhutan country code. Also I don't think widespead usage will justify an exception from the rule or change the standard. Also this would make it stand out really ugly and especially programmers and mathematicians don't like things that are ugly, they like things that are simple, pure and elegant.
XBC (best but unlikely)
in this order.
And then there is also
XZ (country code for iternational waters) ---> XZB
ZZ (country code for unknown territory) ---> ZZB