They're not - the current Armoury System is clearly staying. We know so little about the three new Jobs at the moment so anything discussed is just speculation. But I can honestly say the current class/Job system is staying as is more or less (after all, why implement ROG and NIN like existing classes if they were just going to scrap that a few months later?).

And both Moqi and Akiza already mentioned the reason why your suggestion would not work so I'm not going to add anything further other than saying I agree fully with what they said.