I would not mind seeing the ability to equip you npc with Artifact armor.
Been done like a quest of sorts.
With a choice of all the available Artifacts out there, giving some sort of boost to npc.
ie
SMN AF would boost MP and refresh
WHM AF would boost mnd and cure potency
BLM AF would boost INT and magic attack bonus.
WAR AF boost doable attack and str
SAM AF boost TP gain and weapon skill damage
MNK AF would boost hp and counter rate.
well you sort of get the idea.
This could be done once npc friend hits lvl 60