Well, not a gramp's suggestion in itself but more of an alternative.
We already know that a gramps system like the now dead server most of us came from is not possible due to the fact that leveling is very very easy here.
What I want to suggest is to make something like gramps but instead of exp something more ingame rewarding like instance coins or eden coins without a daily limit as long as you go partying (example), people already farm thousands of eden coins by themselves anyways, why not make this daily task more enjoyable?
Make it also way more challenging like adding mobs with 99% resist, aggressive dangerous mobs like soul panda but with steroids (kek), etc. Mix it with immunity to magic/immunity to physical (so you need to get a party with mages and physical dps), make it hard so that it encourages partying but also make it rewarding (giving eden, instance coins is hardly game breaking or intrusive to the economy or can add any other sort of rewards you see fit).