I might like this. It could be done very well, in a balanced way that allows customization of classes beyond the gear they're wearing.

The problem is how precisely it is implemented.

Option A: After completing a quest, players are awarded 5 "Enhancement points"(EP) used as described for strengthening actions and traits. EP are separate between jobs, but only needs to be unlocked once.

Option B: After completing a quest, players are awarded 1 EP used as described for strengthening actions and traits, there are 5 of these quests, of increasing difficulty. EP are separate between jobs, but only needs to be unlocked once.

Option C: After completing a weekly/daily quest, players are awarded 1 EP used as described for strengthening actions and traits. EP are combined between jobs, so if you play 3 jobs you'll have to decide which job gets EP spent on it each week.

Options A & B could also require players to unlock the points on a per job basis, but I won't duplicate all that text to say so. In any of these scenarios, I think something to reset points would be necessary, like those 10k seals items to reset bonus attributes.

Options A & B would work out like the relic, everyone is expected to have completed them before they attempt serious endgame content. On the other hand, they would end up being "system unlock" quests, and then you would permanently have more customization after that.

Option C would make it like a lengthened leveling/gearing process, you slowly get stronger and customize your character as you get stronger.

Personally, I would prefer something like option A, because I think the game needs more customization, and it could use that customization now.