An ever shifting world..
This sort of goes back to the weather dynamic that occured in XII. When it rained, in some areas, new areas would become accessible and others would be blocked completely, new monsters would appear while others disappear completely.
Could this happen come 2.0? Could volcanoes erupt, allowing rivers of magma to flow along paths that are made then inaccessible, while new one's become open, creatures that are more inclined to the heat are drawn out of the rock to prowl, while others hide away while these creatures and the environment shifts on them?
Could caves and dungeons be made to shift on you while you were within exploring, labryniths that dont set to a specific map at all times, but alter themselves on certain timed intervals, or when different conditions are met (Nyzul did something like that didnt it? I cant remember). Thinking Wrath of the Titans on that one, going down into Tartarus, how it shifted around them. Causing parties to sometimes split into different teams to handle things (I know CC did this, it requires teamwork to make things work, which can be a little frustrating, but I also find refreshing in that it makes people work together better)
The reason the idea came up, is while playing tonight, which I dont log in as consistently as I'd like, I'm staring up at Dalamud thinking.. I wish it could move, gradually. I know its position shifts with the patches and that's cool..but I'd like to see it shift more than that. And with that, there is only a limited window anyways, so they cant really do much. But other things could be done.
The sea level could rise and fall, when the waves pull back certain caves are opened to be explored, when sea level rises those caves go back to being underwater until the next cycle. Just something to make the world appear more 'alive'.