Faldage, has the y'all/ you-all usage become grammatically kosher now? I always thought of it as a colloquialism. And that therefore, all its spin-offs were informal too. So, whilst I agree with you, that the possessive all's simply doesn't hold, I also am left wondering why we must apply rules of grammar *only to the possessive case? Does this help at all?

I too have heard it used as both a singular and as a plural.

Disclaimer: not a member of said contingent; admit to leanings though.