Since the 1960s, there have been a number of new gender neutral pronouns invented in English. Co, hu, and ze to replace she and he. Cos, hus, and zir to replace his and hers. Several academic style guides now allow they and their to be used to refer to singular subjects. Even the AP now accepts they and their as stylistically appropriate. Language is infinitely malleable and is constantly changing. Merriam Webster claims that it added over 1000 new words in 2016 alone. Using grammar rules to constrain new ways of thinking about sex and gender is atavistic.