Final Fantasy Tactics Advanced had Morphers who could shape shift into different monsters and use their move set.
Darn, I was gonna mention some sort of shape-shifting class lol.
Beastmaster would be an easy one since they could use Tamer as the Class and Beastmaster as the Job. They could use whips or something.
Chemist to Calculator would be another combo that I wouldn't mind seeing either. It could fill the gap of a healing class easily.
An old school Geomancer would be awesome, but the implementation seems quite difficult. For example, in FFT maps are quite varied and each one has several different tile types. In an MMO areas are much larger and typically uniform in their scenery. It would get quite boring if you can only cast Ivy for 30 levels unless you fight on that beach over there or that pile of rubble in the corner of the map. Weather is also something that is infrequent and wouldn't be viable as a source of spell variety. I suppose if you learned spells through these processes and were able to use them elsewhere it might be possible...Perhaps storing certain spells for later use?
The only class that I would personally desire though, would have to be Puppetmaster. I don't know what class they could make to go with it, but they could do something requiring crafting classes leveled to a point. this could also tie into Chemist. Edited, May 6th 2013 3:17pm by DamienSScott