somewhat like ldon

[ChaosSlayer]

well as said in first post - you can make a fake instancing.
kind of like Hedge Trials in PoN worked.

its not that complex.
you need:
a. an isolated area
b. a quest npc outside, which will dispawn as soon as group is moved inside the area, and respawn when timers runs out, allowing another gruop to move in.

the fake instance could also be made "dymanics" but cretaing a great variety of NPCs, but only spawning those which corespand to group level (which will be obtained by quest npc outside when group leader talk to npc), and spawn the area accordingly. Of course you will need to create all the npc for level variations intended.

Personaly I would not try fit all 20-60 levels into a single fake instance. 5 levels variations for a single area should be suficient (thankfuly there are crap load of LDON zones)

the part I am not sure of is how to kick the players OUT once timer runs out (my only idea is to spawn an invisiable triger npc with LARGE proximity radius and all players detected will be ported out - not sure if this will work through walls)