Hmm.  Upon reflection I guess I can see the validity of "if you are using the C locale you or the OS are broken anyway, so we'll just pass the bytes through".  I'm not entirely convinced this won't cause issues, but I suppose it might not cause any more issues that having things break due to the C locale does.

It is, however, going to return us to the days when a program that works fine most of the time suddenly blows up in the face of non-ascii data, and that's my biggest concern.

I'd certainly be fine with it if it wasn't the default (that is, programs who need this have to opt in to it).