Yet singular 'they' has been around for five or six centuries, coexisting with gender-neutral 'he'.

One became preferred, or rather prescribed by the same prissy, meddling grammarians that invented the taboo of the split infinitive, in the less than enlightened Victorian era.

I see no reason for us not to shift our preference again in the 21st century, especially as 'they' has the advantage of affording equal inclusion to non-binary members of our society.