It looks like Lightning, as well as some of her friends, will make an appearance in Square Enix' upcoming MMO, Final Fantasy XIV: A Realm reborn. This was confirmed at the Japan Expo that took place this weekend. The only partner of this female fatale that's been officially announced is Snow Villiers.
At this time, no reveal of lore has been mentioned but Yoshida said himself he plans to fit her in properly. After all, she's from the future (XIII), or at least comes from a futuristic setting so fitting her in ARR would be weird. Not because she can't I might add, I just feel she would die from the fashion sense... Don't even get me started on how she'd feel about Gridania. If you do happen to encounter Lightning on your quest, it was also confirmed you can obtain hers and her partners costume and even weapons. (Oerba's spear, please?)
This spark's my interest particularly because names from the Final Fantasy lore are banned from player usage, such as Cloud Strife. This leads me to believe these characters will all make eventual appearances in Eorzea. The development team already said they were going to link all part games together some how so we'll see how this all plays out.
Final Fantasy XIV: A Realm Reborn officially launches on August 27th! Beta Phase 4 is just a touch away and will be open to the public so stay tuned for that if you wish to give this game a try!