In an post on the game's Twitter today, Square Enix announced:
北瀬Pです。windows PC版 LRFFXIII開発状況のご報告です。現在は最終仕上げの段階におり完成まで後少しです。このままですと12月頃に発売ができそうです。秋頃とお伝えしておきながら、お待たせしてしまい申し訳ありません。詳細決まり次第、ご報告させていただきます。
— LIGHTNING ROOM (@LRFF13) October 19, 2015
Roughly translated; the statement explains that the PC port is in the finishing stages of development and that a December release seems viable. The tweet also apologizes for the wait and promises further information.
Lightning Returns is concluding game in the critically polarizing FFXIII trilogy. It was released in November 2013 on the PS3 and Xbox 360.