Just throwing out an idea for a new future zone..

Since ffxiv is set up like a theme park and therefore we won't have small dungeons for the server to access together, how about an idea where a future expansion could contain one or two heavensward sized zones that can have multiple layers of subterranean paths we can travel. Sort of like how O'ghomorro could be if we was able to delve deeper into their tunnels (i imagine their tunnels to be similar to ant colony style tunnels).

Ex1: A typical desert with cities and settlements, include a lost underground city that's connected by tunnels and underground springs.
Ex2: A water zone that has many islands, introduce swimming mounts and dive into multiple huge undersea caverns.
Ex3: The moon, with a boat load of passages to the core of the zone or something like that :P
Ex4: A fricken huge jungle zone with many canopy trees all around. Not to use ffxi as an example because I'm not trying to use it as basis, but their jungles had a few layers to it. You was also quick to get lost in it.. i'm sure se would probably set up more Aetherite or chocobo checkpoints to keep people from getting frustrated.

Connect the instanced dungeons as usual to these large navigable areas for crowd control (you find a random door/gate while opening an undersea cavern, the MSQ reveals that it's a laboratory that you will challenge via df).

This will make ground mounts relevant since you can't fly obviously. This will also probably make swimming mounts a cool thing to have, maybe even the ability to swim as the character. Anyone has any ideas like this?

Send this idea to SE, we need all of this for 4.0!

This is something we really need I'm getting sun burned because there's no underground.

But there should be a big cavern that we can fly in. I'm thinking like the dwarf city in the Eragon series.

Also there needs to be underground areas with mass undead mobs to fight.

Depending on how in-depth the areas are you can even put randomly placed "instanced" treasure chests all over the zone. I emphasized instanced where if one player finds the random chest, it may disappear after opening for them, but still there for anyone else who hasn't been there. Not sure how that would work out though on the technical side as far as developing it lol.

My vote goes for the underground zone.

LALI-HO

I love this concept!

Tera actually has something similar on a small scale they have a zone with a mine/cavern that 3-4 floors deep with little quest hubs in it as well. Think it was called hungry caverns.
At some parts you actually got back outside again on wooden ramps on the cliff side and you could actually look back up or down to see how deep you where was pretty awesome :) plus the amount of shouts in the zone of people that got lost was fun too :P

I would love a mine/cave system or even or cave systems up high in to the mountains. in ff14 heavenward zone or beyond. :D
For new expansion zones you could simply have the base zone available but when you look around in a caves you can see holes in the floor or even the ceilings or walls that you cant reach yet without flight. but when you unlock flight in that zone you can explore extra floors. tho I must say that the mourn/Abalathiafoothils where a good start (multiple path ways and 2 caves even if they where simple caves).