So, essentially, Dark and Darker is a dungeon delving RPG that takes place in a single pre-built dungeon, a single round lasts 10 minutes and the goal is to look gear and treasure to equip and sell. If you die in the dungeon, everything you have on you is dropped on the ground for folks to loot.
Near the end of the round escape portals begin to spawn that will let people escape back to the lobby safely with their loot.
Inside the dungeon are tons of mobs to fight and it's open pvp, so there are lots of wild battles between different classes over loot and escape portals.
What makes me think this would work out so well is that it just needs one pre-built dungeon with pre-set mob spawns and a simple plugin that resets the mobs and treasure chests, and spawns escape objects as the timer counts down. The most complex part is having interesting classes to choose and form a party with, but Herocraft already has a lot of fun and unique classes.
The most recent playtest for Dark and Darker was done via torrent and discord because they are facing a lawsuit for stolen assets, and that playtest, even just being distributed by torrent, hit over 500,000 players within an hour of releasing. And the fanbase is absolutely desperate to play more 'extraction' type dungeon delver. So I think even the most basic dark and darker style plugin would probably fill up a server nearly instantly. (If 1% of the playtest population decided to play a minecraft plugin of the game, that's 5000 people already)
I tried to find a minecraft server that was doing it but to my surprise, literally nobody has yet, but it would be something that would draw a ton of players for what could be a pretty simple plugin.
I started fiddling with command blocks and it seems like I could get it working with those pretty easily honestly with some effort, but a serverside plugin would be more efficient