I think there should be job elements from about... twice as many jobs as there are now.
Machinist, Geomancer, Viking, Sorceror, Statistician, Mime, Chemist, Jugglers, Time Mage/Dimensional Mage-- are some of the more obvious ones that could be created from the ground up.
And I know that there are elements of these jobs present in existing jobs, but frankly these have all been their own jobs in prior titles and could easily be refined into their own unique jobs.
I'd also like to see the introduction of new weapons, particularly flails, but also more unique and specialized weapons like Gunblades.
Some other concepts I'd like to see explored--
an actual defense specialist that can dual wield shields or use huge shields. Basically Paladins without magic or even necessarily a weapon at all.
A job that can possess monster targets to influence their AI (Geists) and/or a Mediator job that specializes in crowd control and monster behavior.
Never been a fan of necromancy but it seems like a fairly popular and simple concept to implement.
A trap specialist.
Wouldn't mind a disambiguation between Archers and Gunners. Hunters, Snipers, Gun Mages... there are a number of ways to do it.
That alone would create another 15ish jobs.
But I really want to see the job system as we know it gone, and I know many other ambitious armchair game designers who wish the same. What I want to see is the ability to combine various elements from all of these jobs into your own unique character.
And can I say one more **** thing about job roles? White Mages, and healer/support roles in general. They do not have to be so obscenely useful. I can point you to many games where you can create a party of four, and whether or not it's even wise to bring a healing job is debatable. The jobs are balanced well enough that a healer is not that much better to have along than a damage dealer. In FFXI this is not at all so, and it's annoying, because there really just aren't that many people who want to play as those jobs in the first place.
Ok, now we're going to get slash fiction of Wint x Kachi somehere... rule 34 and all...
Never confuse your inference as the listener for an implication of the speaker.
Good games are subjective like good food is subjective. You're not going to seriously tell me that there's not a psychological basis for why pizza is great and lutefisk is revolting. The thing about subjectivity is that, as subjects go, humans actually have a great deal in common.