If they add Ivalician Moogles to FFXIV, there's a perfect setup for their existence.

[RitsukoSonoda]

In terms of the world as the game and NPC's are written, playable Loporrits are entirely viable as well. The only people in game that see other players are other players, to every NPC out there none of the other players exist. So a player playing as a Loporrit would be the only one in the world in the eyes of the game world until you reached the moon. Running around on the moon you find there is 1 Loporrit building their own rocket to leave the moon meaning it's entirely possible others had done so in the past. Infact the existence of the Namingway minion gives possibility that it has happened in the past. There are a number of possible scenarios where a wayward adventurous Loporrit could end up in Eorzea suffering from memory loss. And despite you as the player seeing 100's or 1000's of other Loporrits running around everywhere, NPCs would see you as the only weird little talking rabbit out there.

[Iscah]

In terms of the world as the game and NPC's are written, playable Loporrits are entirely viable as well. The only people in game that see other players are other players, to every NPC out there none of the other players exist.

I don't think that's good logic to stick to, though. It would greatly alter the mood of meeting the Loporrits in Endwalker – to one degree for other players and then another level again for someone who is suddenly "finding their lost tribe" rather than encountering an unfamiliar alien race.

And just because other players "don't exist" to NPCs doesn't stop other players from seeing them.

In any case, it's not so much that other players don't exist as that they aren't all WoLs and instead fill the role of random adventurers and townsfolk.