I'll make you a deal, Thomas: If you'll lobby equally vigorously for Jane's use of comma splices [1] [2] as acceptable practice, I'll reconsider the singular "they."
[1] E.g., the second comma in "It is a truth universally acknowledged, that a single man in possession of a good fortune, must be in want of a wife." (Chapter 1, first sentence.) Or the third [EDIT: fourth] comma in "Not all that Mrs. Bennet, however, with the assistance of her five daughters, could ask on the subject, was sufficient to draw from her husband any satisfactory description of Mr. Bingley." (Chapter 3, first sentence.) [3]
[2] https://en.wikipedia.org/wiki/Comma_splice
[3] https://www.gutenberg.org/files/1342/1342-h/1342-h.htm#link2...