Well, see, I was looking this up ages ago, before I started Pieces - and I thought that, too - but in some areas of the the mid-south-west (or whatever that area's called), like Oklahoma, the plural would actually be 'alls y'all'.

This site (http://www.gaylasgarden.com/okie.htm) is where someone has personally deciphered how they speak for on-line friends.

O.o

Kansas!Jamie from Pieces only ever uses 'y'all' as a plural. But Okie!Jamie's half doing it to wind Stacks the hell up anyway! :D