What I mean by this, is what if it was possible to use a max level job to earn experience towards another job?
So, say you have like a level 70 SAM and want to level up a MNK. Instead of trying to slog through level 1-70 (Much of it being dead) on the MNK you could instead continue playing on your SAM after having chosen to "Champion" MNK and earn MNK experience.
The way I see this working, is everything becomes level sync'd experience.
For example, if your MNK is level 5 and you kill a level 70 enemy on your level 70 SAM you'd get MNK experience as if it was a level 5 enemy. If you kill a level 71 enemy as SAM you'd get MNK experience as if it was a level 6 enemy. (Side note: Yes I'm aware that level 5 MNK would be PGL)
This would be the same for quests/duties/PotD/HoH etc.
Thus would inhibit any sort of power leveling shenanigans where you grind out high level dungeons for ridiculous experience gains at levels 1-60, or other such exploitative potentials.
The main downside I see is the whole "But then we get high level players who don't know how to play the jobs!!" though, this isn't a new phenomena given the state of Jump Potions and PotD/HoH spam that often leads players to be wholly unaware on how to play the game...
The other side of things is potentially causing more Tank/Healer players in DF to get fast queues to level up DPS jobs. Though, this isn't necessarily a bad thing given the state of DF queues...