I wouldn't be opposed to a test of personal skill to progress beyond 50, especially one that requires the person focus on everything that's happening and (more importantly) is thematic for each job.

Like a Monk would need to use Dragon Kick at the right time to Pacify a dangerous opponent's weapon skill, or switch his fist stance based off his opponent's shifting elemental weaknesses. A White Mage would have to keep an ally alive while being attacked by other enemies (sustaining himself and an ally under pressure). A Black Mage would need to rotate between crowd control and elemental spells while kiting to bring down a group of enemies alone (too tough to AoE down, too tough to Sleepga + kill one, kill next before Sleepga's diminished effect kicks in, etc.) Just as examples.

Frankly if this fight would be just "run up to the guy and hit it until it stops moving" then it'd be nothing more than irritating busywork and a gear check. That's not fun.
(This whole thing reminds of me of Cecil becoming a Paladin in FFIV, and how that was themed to the Paladin job quite nicely.)