I think I read that NPC characters from Grand Companies will be included in the future to do Duty Finder or something like that... Maybe that's a way to have what you want. The game already has Lightning, Snow, Iroha, Cloud, Firion, the Warrior of Light, Zidane, and Setzer's clothes (besides another FF14 characters like Odin or the Scions). You could customize those NPCs to resemble those characters (and the game also has Lightning, Odin, and the Scions' weapons, and the Emperor's New Fists for Snow). Also, with the help of dyes, you can dye gear to create NPCs resembling Vivi or the Onion Knight for example. Obviously, this would be possible if those NPC are customizable.

The only thing you need is... gear. And FF14 is always getting new gear from other FFs, that's one of the reasons why I consider FF14 a tribute to the entire series.