I would love to see a few more of the Job Characters show up in the main storyline. Although it really depends on the particular Job NPCs...some of them would be relatively easy to put in the main plot, but many others would honestly be pretty difficult. So I might bring up a few Jobs whose NPCs I would probably not expect to see in the MSQ...

Scholar: Not only are some of the most amusing ones Tonberries, and thus kill on sight in most areas of Eorzea, they also have a pretty insulated questline about Nym. Not much reason to unless we have a whole expansion based on the War of the Magi (which I wouldn't mind to be fair...)

Bard: I could see Sanson and Guydelot making a small cameo if we ever needed an important Gridanian military unit to show up, but other than that I don't see them making much of an impact on the plot. Their adventures are usually just fun little tales rather than epic world changing events anyway.

Black Mage: The Shadow of Mhcah storyline was probably the most important that Black Magic has ever been...and they didn't show up there. So I doubt they'll show up much elsewhere.