It was made pretty plain in 2.2 that Yugiri was the first Ninja to offer to train anyone in Eorzea seeing as she said she would start teaching graduates of the rogues guild and no one had seen her fighting style before. Why would she offer such a thing if the Eorzeans already had it? Why would they accept her offer in such surprise if they already had it? Why are there no Ninjas in Eorzea already if Yugiri is not the first? I don't understand why people are trying to make up reasons why it would be possible to unlock NIN before doing that story quest when it so plainly makes zero sense.

Considering that FFXI gated ALL but the six starting jobs behind storyline quests (i.e if you wanted to be a SMN you had to start as another job and unlock SMN later) I see it going the same way here. It would just make zero sense for anyone to be able to become a ninja before they'd completed the quest that actually introduces ninjas to Eorzea. It'll be the same for any new classes in Ishgard in the expansion.

At a stretch I could see the Rogue being available to new players but even that guild had kept itself hidden until Yugiri made her offer and again it would make no sense when that player reached the 2.2 story to have the 'revelation' of the rogue's guild after they'd been a part of it since the start.