In an E3 2013 interview with 4Gamer.net, Yoshinori Kitase revealed Motomu Toriyama was the one behind the Outerworld Services in LIGHTNING RETURNS: FINAL FANTASY XIII. You can read a summary of what was then said below by Twitter user @bk2128 with light edits by me.
After Kitase revealed Toriyama was the one who added the Outerworld Services, Toriyama added he wants to prepare for the next generation [of consoles], but also put an emphasis not on communication with friends like in SNS or MMORPGs, but rather on giving the feel that there are also other people playing the game despite it being a single-player game.
Toriyama believed next-gen consoles would have stronger features to share something with other players. The reason why he added the Facebook link feature to LR was because if they made the challenge right at that time, they’d be better prepared for the next-gen consoles.
Kitase added the current Facebook post system (in LR) would enable receiving Potions from other players, but in the future he’d like to evolve (read: apply it further) into other items like weapons. For example you can receive a weapon from another player, then use it to strengthen yourself, and when you don’t need the weapon anymore you can give it to yet another player. If the weapon gift cycle is continued to about 100 people it’d be very interesting, especially if there’s a history list detailing from whom to whom the weapon is given.
Will be very interesting to see if they’re able to evolve this on PlayStation 4 & Xbox One.