My prefered idea is to have AF2 (and perhaps maybe AF3) as quest items (if they do increase the level cap) as a reward for advancing a continuation of the job storylines and relic armor as sort of uber gear from a super dungeon which can be upgraded. For example, AF2 being reskins and relic being entirely new looking gear.

Maybe even have it go like AF2 at levels 71-75 and AF3 from 95-99, then have relics upgradeable from level 80+ from a mixture of crafting, questing (perhaps even visiting the job storyline quest givers) and high level FATE encounters.