As great as FFXIV is, it fails to capture the "wonder" or "exploration factor" that FFXI had. There is an emotional feeling attached to getting through a dangerous labyrinthine cave/dungeon/tunnel only to arrive in a vast/beautiful zone, and eventually stumble upon a hidden outpost or village. FFXI pulled it off multiple times with Rabao, Tavnazian Safehold, and Norg.
FFXIV is not FFXI though. You can reach any area in the game in minutes (or less) via ports and mounts. There is no real danger in the world. And aside from the story (which was great), you never feel like you are on a legit adventure.
So why not create an optional zone in 4.0?
Make it lore-heavy, with optional daily side quests
an optional questline
and a number of beautiful sightseeing opportunities (places to RP)
For example:
15min ship ride to an island
Told that the ship has no room for mounts (justifies lack of mount use in the upcoming zones)
Chance of sea serpent / leviathan attack on the way
Can fish on the ride
Can play Triple Triad on the ride
Once you arrive at the island there's a small outpost with some hidden spots (like a small cave along the beach with a grotto) for RPers
Then you have an entire rainforest zone, with twisting hallway-esque pathways, tunnels, pathways up into the trees, etc. Lot's of super pretty hidden spots for RPers.
But the mobs are actually dangerous, block paths, and have slow/bind moves (so people can't just run through everything). You can solo them but it takes time.
Multiple caves that seemingly lead to nowhere, or have monsters in them, etc (kind of like the old 1.0 zones)
One cave that leads to a hidden beach and pathway through mountainous terrain
And then a village at one part of the pathway, with a lot of lore, lots of rp spots, and lots of hidden stuff
OR another example:
A mysterious train service is set up from an abandoned imperial outpost (using their rail system)
You take a 15 min train ride where ghosts spawn and attack
Chance for a special boss spawning
Can play triple triad with some ghosts
Lots of lore about the mystery of the train
You finally arrive in a wide open rocky valley between mountains, no trees so beautiful view of the sky. Small mountains and hills that can be climbed, or have caves. Huge mobs that take 5 or 6 people to defeat (not necessarily high damage, but tons of hp or defense).
Some beautiful weather effects.
Dangerous ghosts and demons that only appear at night
A beautiful temple carved into the side of a mountain wall, with a makeshift town inside it (e.g. Ala Mhigans who escaped the empire)
And night-time fates where the city is assaulted by demons/ghosts/skeletons
An intricate emotional adult story about death and war, with a death-like open world primal (because we were all looking forward to open world primals)
etc.
TLDR; 4.0 should have an old-school MMO-esque zone, that you can't port to, that you can't use mounts in, that has dangerous mobs, and that is -unique-. Something that violates the cookie-cutter design of the rest of ffxiv. It should feel like an adventure, be designed with RPers in mind, and be purely optional