I think this could work, but it would take an insane amount of development. What you're talking about is basically rebalancing every single job to be suited for multiple roles. It takes us back practically to scratch for balancing.

Personally, if we're going to go back this far, I would rather them remove the "armoury system" and allow jobs to wield different weapons. Warrior for instance should be able to wield nearly every weapon imaginable in my opinion.