Not sure whether this has anything to do with what you're asking, Faldage, but let's think about how 'you all' evolved. It could be that it was simply a short cut for saying 'all of you'. If so, we could write:
"All of you should listen."
Well, that was just too wordy. So, here in the South we cut to the chase and said,
"You all should listen."
And, finally:
"Y'all should listen."
"You all" began to function as a compound pronoun, so to speak. And so did "y'all" rather than as a pronoun followed by a modifying prepositional phrase as in 'all of you.'
When looking at the possessive form of 'all of you'--well, we've got a slight problem that we can address by changing 'you' to 'your,' obviously:
All of you should listen.
All of your children should listen.
All of yours should listen.
You all should listen. (compound dialectical pronoun form)
You-all's children should listen (compound dialetical pronoun now taking adjectivial form with apostrophe at the end of the compound form)
Y'all's children should listen (the compact edition).
That's how I see it right now, but will wait for further elucidation.
Bill, I never have heard anyone here refer to a singular person as y'all.