What if the clover in the hint isn't green mage but...

[Fyrebrand]

It could be for a Druid job class that make it another healer class. 3 leaf clover was a sacred plant to Druids.

That would seriously be my dream come true! Would instantly be my new main. I think it's already been stated the new jobs will both be DPS though -- specifically a melee and a caster.

Okay, crazy not-serious new theory: new job is "Gambler" similar to the "Lady Luck" job in FFX-2. That's not a three leaf clover, it's a club symbol, like in cards. The TMNT shirt was hinting at the four suits of playing cards, since there are four turtles.