I would be surprised if the Job system wasn't out by PS3 release, it provides a really good concept to show off for advertising it. Also, I feel it is safe to say that SE has been working on the job system since at least 2/28/11 since that is the date that Yoshi let us see some nice what also is safe to say concept art for Job specific equipment for two of the jobs that are likely to be added.

Also, iirc all of the battle system changes are supposed to be implemented by the end of the summer. The job system is a huge concept of the battle system seeing how SE wants job system to be group oriented while leaving the current class system for solo play. If SE doesn't release the basis of group play for the battle system they will be unable to create any end game content / dungeons that are challenging like Yoshida says he wants to make.

I am going to make an assumption that the Job system will be implemented in 1.19 or 1.20 (Which I am guess is going to be the patch that prepares for the PS3 launch.)

EDIT: Or in other words what Xeno said... lol