Interesting chart there. Dark Arts, well DK uses it so not sure how it fits here.
I think the chart was more likely very early on and they have since then decided to go a different route for classes and future jobs.
We seen that when Muskateer which many figured we would have but ended up with machinist instead. So i guess they are not afraid to change things up from previous FF games.
I really think Blu Mage will be the next job added, perhaps with Samurai?
In all honesty i dunno why so many want Samurai so much, i could care less and would rather see dancer