One word only:
From private communication, I have been told to expect the
revised version of ISO 639 sometime in 1995.
Anyway, about 3166 codes: I think they are rather safe to use
for most purposes - and the chance that a code (such as SU) that
has been in widespread use is going to be reused for some
other, unrelated country, which is the one scenario that would
really mess us up, is practically nil.
After all, the ISO people are not wantonly destructive.
(....? :-)
Harald A