A floating Island could prove problematic if it drifts away from your ship. But is there ever a time that everyone is off a ship at the same time?
A floating island could be cool if you are marooned and then the island you're on takes you to weird seas.
A floating island with a legendary location seems most interesting. Some rare thing that might break the campaign if too easy to find. "Yes, we found the fountain of youth, but when we return to civilization we won't be able to lead anyone back to it." Some ideas:
- magic fountains
- shrines to forgotten saints
- trees with magical fruit
- rare beasts
A floating island is the ultimate place to build a wizard tower especially if I can figure out some means of propulsion. Then I can travel to the icy north, visit various lands offering my services and gathering ancient texts. Of course by that level maybe I can just teleport around.
What would interest you about a floating island?