I kind of think though that if the jobs had a totally different skill set to the class then they would basically lose all association that connected them to that class in the first place. and that being the case there is really no need to have jobs stemming from classes at all they should just be entireley seperate entities.
given an example. if you develop your thaumatage to max level as a thaumatage then you become a thaumatage master. but if you then unlock blackmage youve instantly become a black mage master there was no levelling / learning process involved in that mastery. you could say it tooks you hundreds of thousands of exp and a lot of practice to become a thm but to be blm in a few simple quests.
not to mention the nightmare of new job implementation. where for every job you release you would need a new class to go with it. thus you end up with 20 jobs and 20 classes or. you end up with a scenario where if they are going to tie second jobs to the existing classes then they need to release 8 jobs at once (or how ever many classes there are). if they didnt then you have a huge unbalance where one class has 2 job options but another class only has 1.
some people have said have them the same till level 20 then totally seperate them. there was a recent thread where thm becomes an enfeebling specialist blm becomes elemental. it would be just as easy if not easier to just seperate them entirely and make that enfeebling specialist a redmage or whatever build them both on a unique frame rather than trying to twist one frame into several different things.
another thing i dont like the idea of is that lets say a year from now february 2014 every class gets a second job. then bam i have 8 more jobs at max level and i didnt even have to kill anything. burn a few quests and i'm a master at them all. which kind of sits badly for new players if the older players never have to level anything again. (save for a cap raise)