Singular y'all (and yuz)?

[Mark A. Mandel]

Dennis Baron writes:

        >>>
perhaps you guys is just a new marked plural, but what role is it
filling if y'all, yins, and youse already function as effective
plurals? My theory--please someone do research--is that y'all has taken
over, thru politeness constraints, the functions of sg. you as well as
pl y'all, hence the need to move to all y'all or you guys,
        <<<

If they're not used by the same populations, they don't affect each
other. If "y'all" is southern and southwestern, "yins" is central, and
"youse" is NYC, then "you guys" can fill a gap in the rest of the
country... not to mention different segments of the population, by age,
class, or other dimension, within the aforementioned regions. Of course
this reasoning works whether or not I've accurately described the
dialect ranges.

-- Mark A. Mandel