Originally Posted by pdurrant
Now that it's more accepted that they (etc.) can be used as a singular pronoun, their use will become far more common. And so become even more accepted.
English has, on the whole, lost the distinction between the informal/formal singular/plural second person pronouns "thou" and "you" (although "thou/thee" is still alive and well in some English regional dialects, such as the part of the country where I live). The same could perhaps happen with third person pronouns, although I personally doubt it.