There are various RPG scenarios that have used island cities (e.g. the Imperial City from the D&D Birthright campaign), but none I can think of that have floating islands.
I would like to see
- a mining site with poppet heads and pumps
- "rocket" (probably based on A Trip to the Moon or something similar)
- iron golems "working" somewhere
- a park
- sewers and drains
- multiple islands at varying heights
- housing of varying niceness
- streets and shops
- alleys and courtyards (cf. The Royal Mile in Edinburgh)
- and probably more when it comes to me
I would make there be a main island, with a separate mining island. Some islands would have pipes and railways connecting to them Some would use bridges. Given the sewers etc, we would want to develop the underneath part of the islands as much as the aboveground bit. Some islands may have liquid spilling out and onto other islands, providing another transport route. Elevators are another option in various parts.
I think that once we get the basic aspect of the plan organised, we need to make sure that we don't go too overboard and try to design a continent. Perhaps start with three main islands - upper class, industrial, mining and start from there. Other parts can be added as we go.
And I have no idea what weather/biomes occur on a flat world.
Mechanically, I can think of things like:
- retracting bridges
- rotating hands on clocks
- moving artwork
- lighting systems