Their as a gender neutral pronoun, while a grammatical catastrophe, has been around for a long time and isn't rooted in SJWness, but rather used to specify a hypothetical person for which the gender isn't known.
It's ugly and stupid, but its origins aren't PC garbage. I remember hearing, and recoiling to this, long ago
Actually, use of their, which is a plural pronoun, in situations where a singular pronoun is correct IS a product of the same thought control movement that gave us social justice warriorism. It began with the movement in the 1960s of "avoiding sexist language."
When I worked for NRA we got new dictionaries. In the back was a multipage section explaining how to avoid sexist language... use chairperson instead of the violent thought rape term chairman, etc.
The use of their as a means of avoiding use of the more specific he/she was also discussed, and was recommended even though it was a violation of extant grammar rules.
Tragically that section of my new dictionary did not survive an encounter with an X-acto knife.
But, the usage is gaining increasing traction, and is showing up as an accepted non-standard usage.
It's even showing up on dictionary.com...
(used with a singular indefinite pronoun or singular noun antecedent in place of the definite masculine his or the definite feminine her):
Someone left their book on the table. It's good for the teacher to have high expectations for their students.And yes, it is incorrect now, but it is changing, and becoming more accepted by more and more users, which is how languages and their associated grammar rules change in the first place -- not by the actions of some committee (unless you're in France or Iceland).