Full month names would be encoded in encA. Currency symbols in encB. Is it a good idea? No.
>Should the setting not be one for encoding (selected from a range of encodings), then settings for formatting and messages (selected from ranges of locales), then finally a setting for collation which is both a locale and an encoding?
I would argue an encoding setting should not be there to begin with or at most be application specific because that really doesn't depend on system locale (as long as the signs used by the system locale can be represented in the encoding used by the application).
I was just explaining why LC_* should exist even on a strictly UTF-8 everywhere system. I never said storing the encoding in the locale was a good idea (nor is it part of the official locale specification - it's a posix-ism)