Spoke to the dev. team to try and wrangle some more details regarding the upcoming job system. The current thinking is to have one job for one class. So for example, if you are a gladiator, the job you could unlock would be paladin, etc. Right now, we can't give any further details about the possibility of having multiple jobs per class.
To try and stave off the coming flood of "So if gladiator becomes paladin, then what will xyz class unlock?" You'll have to stay tuned for more details in the future!