the thought occured to me: mmo's map design is always horizontal and never truly vertical. Very infrequently are we spending time on different levels such as an underground, ground-level and above ground area. There will be small areas in which there is an underground area, but the whole of mmo design doesn't accomodate that.
Think of WoW, there is the Undercity which is underground and has different 'levels'. It still takes up a separate area than the rest of the map as in, nothing occupies the highest lvl of Undercity, just invisible walls.
When I think of Rift, there are castles in which corridors have multiple levels. The Defiant captial, Meridian, has a mage tower with multiple levels separated with teleporters and tries to give the sense that you're going higher up. There is Lantern Hook, a high lvl city which had levels hollowed into a huge rockface. Scarlet Gorge was a great example of giving a sense of depth; being at the top of the gorge or at the very bottom, or even areas underground.
Think of WoW, there is the Undercity which is underground and has different 'levels'. It still takes up a separate area than the rest of the map as in, nothing occupies the highest lvl of Undercity, just invisible walls.
When I think of Rift, there are castles in which corridors have multiple levels. The Defiant captial, Meridian, has a mage tower with multiple levels separated with teleporters and tries to give the sense that you're going higher up. There is Lantern Hook, a high lvl city which had levels hollowed into a huge rockface. Scarlet Gorge was a great example of giving a sense of depth; being at the top of the gorge or at the very bottom, or even areas underground.
Aion did a cool job with flight and having items of interest floating in the air.
But look back at that photo.
Imagine an mmo world where (say, for example) you started off in the underground area with plot talking about how one day instead of looking up into the sky, you'll find a way to the surface and be able to look down from where you came from. A truly two-plus level game world. Instead of looking at how big a mmo's land mass is, one will need to take into consideration of the underground AND above ground areas that occupy the same space. Sure, this concept (especially above ground areas: think floating islands) may not be applicable to some lore, but it can in many fantasy settings.
This reminds me of rpg Neverwinter Nights: Hordes of the Underdark. You started off in a tavern of sorts and you are forced to dig deeper and deeper in the dungeons/maze to find the villan. It felt like you were getting incredibly deeper instead of going farther in distance away from your origin. But as a D&D type of game, its levels are not truly connected as an mmo world normally is (no loading screens).
I understand the trepidation of designing such a world though; people have a hard enough time navigating the normal game world, hence the need to indicate waypoints or have a map that shows where to complete quests. And that is only on one plane of design; I myself get confused sometimes when a quest navigator shows me where to complete the quest and I don't realize the quest components are hidden underground. That, and for some people navigating different levels without a defined 'ground' and 'sky' may cause nausea.
