Area for Samurai and Ninja

[Kirito]

What's the reasoning behind a ninja class having a samurai job? In popular lore (which the FFXI samurai is based on) samurai and ninja are pretty much opposites

They have mentioned they were looking into adding more popular FF jobs, including ninja and samurai, and they've also said they were looking into how to add them, and whether it's doable to have multiple jobs per class. If they go with multiple jobs per class, samurai would be a job for either warrior (very likely) or archer (not very likely, but historically more correct ), ninja would have to be a job for maybe a rogue class. Rogue class could also get thief as job.

That's all just speculation of course, and we'll have to wait until they actually start implementing more new jobs before we know anything. We're already getting summoner, and I believe musketeer is a given to be the next new class/job considering there's already content for musketeer, or at least, there was content for musketeer in 1.0

Yes that would be if they decide to extend the job ranks even further... If they don't decide to then I would think they would have ninja extend to samurai since they could relate the story of the extension quests with ninja and samurai together... plus it is not the first time they had one class extend to a non-similar class. Arc/Bard