Going to start off by saying this isn't a thread to get rid of classes. I just can't imagine how new jobs would feel unique if they branch off of current classes. If you have a serious example of how, for example, a thm could branch off into anything else and still not use the same thunder>thundara combo for the majority of its time and damage, I am beyond happy to hear it.
I'm not sure if anyone has brought this up in the past; the idea is to tone down how many skills that you naturally unlock from being a class and give most of them to the jobs.
I'm not sure exactly how the specifics would work, but, in theory, the current jobs would not be changed in any major way and classes would be more refined into something that is a building block instead of fully functioning, self-sustaining entity.
The concept is that jobs would unlock most of the abilities usable by said job instead of the small portion unlocked with the current system. Classes should still get the basics and, with more freedom to cross-class, be able to function in endgame content if people are inclined to do so. Maybe something along the lines of the major combos are unlocked by jobs.
Using Thm as an example again, it wouldn't unlock any spells beyond Thunder, Blizzard, Fire, and for arguments sake, Thundara (I personally don't think the class should get thundara in the proposed system, but I don't see how it would function competitively without it.) An example for Cnj would be it doesn't learn Sacred Prism or possibly Cura. Gladiator wouldn't learn any of the shield abilities, naturally. Perhaps Warrior learns all the defensive/tanking abilities that Mrd currently has and Mrd learns the offensive abilities. Monk would learn all the elemental fists and I'm not quite sure how Lnc would change. These are just some of the changes, not all the abilities that would be switched around.
The only way I see it working is if jobs were unlocked at an earlier level, something around 20, so that they have more time to work towards their abilities. Again, in a perfect world, jobs would stay the same in practice, and classes would be more refined from where they currently are.