I'm pretty sure the jobs we're getting will work something like Rift's system but much more flexible, essentially jobs within classes. I can't see them adding, for example, the Summoner job without first adding an Evoker class first, or something similar. And I'm fairly sure I remember them saying that no new classes are planned for a while.

That's not to say that we'll never see them though. What's obvious is that we will need to see new classes before some of these jobs make an appearance.