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.

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Lightning Returns is concluding game in the critically polarizing FFXIII trilogy. It was released in November 2013 on the PS3 and Xbox 360.