I do like that idea. Ihate when I find something good, then needs to be replaced just because its "outdated".

The first AF chast piece as a Blue Mage in xi had +15 to blue magic skill and the second AF didn't have that boost, which watch pretty depressing since it forced players to still use the outdated piece . It would of had been awesome if I was able to level it up.

For this system I would want the item to actually level up, just like us, with an exp bar and everything.
So each time the job specific gear levels up, the required level goes up, and stats of the gear would be regenerated at that level.