I finally made the hardcore mode - which is now called Eternal Unrest - available for players in game. To enable it you need to put Nolanoths Blood and/or Witch Dust into the statue in the Devils Bluff ruin. Next to the portal stones of course.
Each Nolanaoths Blood increases the Eternal Rest Mode by 50%. Each Witch Dust by 10%. The maximum is 100%.
The percent chance determines if a monster in the Abyss gets a second life after you killed it and it affects your rune drop chance. So if you set the Eternal Rest mode to 100% you get doubled runes and doubled spawns.