Object demand problem occurs where single-player RPG patterns are imported into multiplayer(especially massive open world).
Typically the problem(aka "waiting in line") is present when multiple players in same location have to get exclusive access to something(object/npc) or to move into specific location.
e.g. quest for many players requires to do X at location Y, which can't handle them all at same time or has other limits that force others to wait their turn.

1.Shared instance:only player in party exist in the location.
Limits access to specific group or player himself.

2.Shared world instance: all player touching the object/npc/location can use it at same time.
This simply removes exclusive access. Some immersion breaks will occur, such as many players completing one quest repeatedly.

3.Remove the shared object: either removing the need to get near the object or moving the functionality into UI dialogs. Removing problematic quests is also an option: many single-player quest mechanics simply don't work in a shared world or look awkward and forced(especially when player repeat the quest on new character).