Personally, I believe the problem resides in the term, "you" as second person plural to begin with. It sounds singular, which is why there are so many 'fixes' for it.
Which means we are less offensive than the damn yankees!
Regarding southern usage: it depends :)
I was once informed that “y’all” is singular, and “all y’all” is plural, and that furthermore, “all y’alls” could refer to a group (club membership, ethnicity, sports team fans, etc.).
American English defies codification into a rigid grammar :)