Darkest Hour

So, we have the Dying Earth. Now try to think about making similar setting / some world inspired by it. Or even try to push it little further.

This is my rather chaotic list of things that may be the most interesting and / or challenging parts of designing worlds during their Darkest Hours:

• World is Incredibly Old. It means that its moon probably flew away or was ripped apart by planet's gravity, which can cause dramatic and unpredictable climate changes, planet's tectonic activity has stopped and thus world is generally much, much flatter than now - mountains were reduced to hills. No earthquakes may mean that planet is holed by incredible number of caves, rifts and ancient, artificially created tunnels. Spelunker's heaven!
• Not Only Sun is Dying. Fabric of reality is weakened and torn in many places. Demons infested the world, magic is strong, probably much stronger than technology. But everything has a price - magic is generally evil / unpredictable / dangerous to use.
• Technology has Failed - why not? We want the fantasy / science fantasy setting, not some ultra-tech rubbish! :D
• Most of the Species has Died. Climate changes, fucked light wavelength and demons roaming the earth has major impact on planet's fauna. This is the part I like the most - try to design all animal life still known by humans! Moreover, limit the number to several dozens :D I fucking love game design.
• There are Surprisingly Many Sentient Beings. Kinda obvious - they were smart enough to survive. And they were evil enough to survive.
• Most of the World is Uninhabited. Humans retreated to one region. Travelling from town to town within the borders of these "1d6 Kingdoms" is still dangerous but try to imagine how deadly the environment must be outside that safespot. Of course, there are 1d1000x27 reasons for adventurers why they should go and explore those unknown, forgotten lands.

Any questions and / or ideas?