Thou shalt use proper pronouns and not be lazy recycling plural pronouns in the singular. What next, are thou planing to use a singular "we" like inbred royalty?
The point isn't to say that the singular they is somehow better than the singular you, it's to point out that it is not a modern invention. People that dislike usage of the singular they often argue that it is an unnatural change being forced upon the language, when in fact it has been in use for so long that it was used by Shakespeare