Concept 1:

Basically weapons or armor that require a sub job to use rather then the main job.
Example: Can't use this piece of gear unless your sub job is THF.

lv99 "?????? Ring"
Required THF Subjob to equip
(Whatever stats)

Concept 2:

Pieces of equipment with added stats that say for example:

lv99 "?????? Ring"
All jobs
RDM Subjob: (Whatever stats)