Yoshida said somewhere (I want to say it was Fan Fest, maybe EU?) that Zhloe was a test and they planned to expand the system if she was a success. So from that I'd assume they hadn't worked on any additional NPCs yet at the time they released Zhloe, so there will be a gap before any more are ready if she is viewed as a positive addition to the game. I liked the system so I hope they add more. Yoshida also said something about potentially making gear/weapons etc for NPCs and having the NPCs start to use the items you made them to make crafting feel more rewarding.