"Y'all" provides the differentiated 2nd person plural pronoun that standard English does not have, unlike most other European languages. I wonder if the researchers would have received any hits on "yous" or "yous guys" from major cities in the north east? There is another Texas phrase, "all y'all" to differentiate from a limited number of "y'all".
It's not easy to be spelling police on a word that isn't in the dictionary, but please note that you misspelled "y'all" in the title of your post. Being a contraction of "you" and "all", the apostrophe comes before the "a", not after, although I've seen it misspelled that way often.
Actually it is in the dictionary and it is recognized now as a word. It's a somewhat recent development though I forget exactly when. So y'all can rest assured in the Hippie home that it is a legit word.