Singular y'all

[sagehen]

The formulaic "y'all come back, y'hear?" at the end of commercial
transactions that I was hearing for the first time when we moved to
southern Ohio from the west coast, was equally addressed to singular and
plural customers.  I don't know if it has been entirely replaced by "have a
nice day" in its old haunts, but wouldn't such automatic expressions be
likely to have spread out into general usage?
A. Murie