I know that for some languages there is maybe not only one choice
 of (input/output) encoding, but this doesn't mean a default cannot
 be chosen. In my opinion, a default that suits a large proportion
 (even a minority) of people is better than a default that suits nobody.
 Don't you agree?

I don't. I think that your point is interesting for default output
encodings (but, imagine that i install many fonts only as T1, what
would happen to me in language nohyphenation or english??), but not
for input encodings.

Maybe babel could emit a warning when you try to typeset some language
with not suitable encodings?

Thierry Bouche, Grenoble.