A moving/dynamic zone would be cool (e.g. a ship or train)
Anyone who has played FFXI probably remembers the selbina-mhaura ferry, sea horror, and the pirate attack. There was also a similar ride on a barge through the Phanauet Channel with multiple pathways.
There's something fun about a zone where you're just on a vehicle, with random events happening during a trip. And it could be something unique and simple that makes FFXIV feel special and more memorable.
Since servers are more powerful now, it would be awesome to have a myriad of different random events and random paths for a boat to travel. Or to have something completely different like a train ride across the main continent.
Either way, FFXIV could really use some unique non-cookie-cutter content.