While the "you-all" strategy certainly works if it is applied universally (which it doesn't; other strategies, such as "you guys" or "yinz" are used in other areas of the country, and "you-all" has been spotted in the wild being used as a singular) it has not been accepted in Standard English.

A similar strategy to Tromboniator's 3rd person singular verb with singular "they" was used in the early days of singular "you". It did not last. The verb form has followed the pronoun and not the person and number of the pronoun.