FFXIV being a story-based MMORPG, there is of course present the contradiction where both everyone is the hero who saves the world and only you are the hero who saves the world, depending on whose point of view we're looking at, the players' or the NPCs'. However, we are often told, by said NPCs, things like "Gather your adventurer friends", which means the story does indeed acknowledge other players' existences.

So, I thought up an idea on how to integrate, if only slightly, other players into your story. In areas where each player gets their own private instance, like the Waking Sands, Rising Stone, and House Fortemps (and maybe even temporary instances like that gathering at the Sultana's at the end of 2.55), populate the area not only with their standard denizens, but with a small handful of NPC copies of players on our Friends' List.

They wouldn't do anything but loiter about, repeat an animation, and have some lines to say when you click on them, but it would add a ton of flavor, and be fun to talk about with the actual people, like "Hey, I saw you at the Rising Stones with Hoary Boulder. I think he likes you". For extra flair, the lines and actions could vary depending on things like race/gender/clan/job/etc. And if it bothers anyone that technically a character would be in two places at once, have it gather the list of possible candidates from only those friends who are currently offline.

tl;dr I love the various NPC interactions in the Rising Stones throughout the story and they should mix in actual players with them. It would be cool.