Let's not preclude a future Thief job - it would be quite fitting for the thief to be portrayed as a L30+ event, where you are pulled aside by a master thief and trained in unsanctioned skills.

As for Ninja, their use of symbols makes me suspect that the Arcanist will be the required subclass, due to their use of symbol-driven arcanima, while the archer's quelling and raging strikes will come front and centre as the third class' available skills.