Fresh classes.

[Gormogon]

Peace Agent: No weapon. Uses the soothe command to pacify the enemy. Uses doubt to scold the enemies. Uses pose to amaze the enemies.

[Kitru]

Great Katanas were the two-handed weapons used by SAM and modeled after the real life katana, while the Katanas were the one-handed weapons used by NIN and modeled after weapons like the wakizashi.

Actually, Ninja used the Ninja-to. It had a shorter straight blade compared to the wakizashi's curved blade, which allowed for the scabbard to be used for other purposes (a curved scabbard is actually pretty weak thanks to physics). Wakizashi was specifically the small sword of the Samurai daisho (lit. "big-small"; the pairing of katana and wakizashi that were the trademark equipage of the Samurai to such an extent that wearing either when you were not of the caste was a capital offense). Calling it a katana is like calling an English longsword a scimitar.

It's for this exact reason why you actually end up seeing the ninja weapons called "Ninja Blade" instead of some variant of "katana" in FF games with both Ninja and Samurai (in those games with just Ninja, Ninja use katana because there's no need to distinguish between the specialist swords of the two class/jobs). If both NIN and SAM are added, NIN should use daggers and/or ninja blades, which is what they have historically used in the FF series for those games with both SAM and NIN, and SAM should just use straight-up katana (likely just a single one in a 2h grip because, in the FF series, dual wielding has been the providence of ninja).

Also, random note, the larger "katana" designed to be used only in 2 hands as opposed to the hand-and-a-half (one or two handed) design of the katana were actually nodachi (lit. "great sword"). There was no such thing as a daikatana or great katana because katana referred specifically to the large portion of the daisho.

The problem with Ninja and Samurai both coming from the same class, however, is what Exstal already paraphrased from my points on previous discussions (which he seems fond of doing, given his signature): a Ninja and a Samurai fight in completely different ways, to such an extent that any job change would require such monumental changes to the base class that it would require as much work as simply making a new class entirely (new animations, new attacks, modified CDs, etc.). The only link between the two is the asian theme, which is not enough to have them stem from the same job.

[Kitru]

An Onion Knight style class that gets stronger based on your number of level capped jobs would be interesting. No idea how that would fit into the Holy Trinity, though.

There's already something like this in game insofar as you can run as a base class and use 10 CC skills drawn from all of your classes instead of a job with 5 drawn from 2.

However, if you're talking about a class that actually grows in power based upon your number of maxed out jobs/classes, it would be broken as hell. It would need to be balanced around having all jobs maxed out because, otherwise, if you maxed out all of the jobs, it would end up being stronger than any other job. At that point, it then becomes weaker than any other job until such time as you have maxed out all jobs.

Onion Knight/freelancer works in other FF games because they're single-player games where balance across classes isn't really needed because you're not competing against anyone else. Freelancer starting terrible and becoming the greatest fighting force in the universe is simply a reward for completion in a game where completion isn't really required. It's kind of like the ultimate weapons found at the bottom of the uber-dungeon after the uber-boss: you've already beaten the only thing that said weapon would actually help against, so it's only really there as a "you are this kewl; have a badass weapon to show off and demonstrate your awesomeness" feature.

The same logic is there for elemental weaknesses in MMOs as well as a bunch of other stuff. MMOs absolutely *have* to be balanced amongst the classes so as to not render one or more classes irrelevant for running content and play has to be both fun and approachable so a lot of the classic tactical/mechanical options that other games used are outright impossible as well.

Honestly, when considering mechanics, it works better to think about ARR as an MMO, rather than a Final Fantasy game. The theme/aesthetic can be derived from FF, but the mechanics most definitely need to be MMO.