A Spirit World you can enter through Ancient Cities!

With Ancient Cities being added, there's a possibility for a new dimension being added with the very portal-like shape that resides in these cities. With the deep dark being a scary place, it would be nice if you could use the materials found there to craft a spirit portal! The spirit world would be a brighter, but more corrupted version of the overworld. Everything looks messed up, blocks are in weird places, etc. The hostile mobs could even be the spirit of zombies or skeletons lurking their world! There would be a new boss much like the Ender Dragon or Wither, but you'd have to find where they lay! In order to enter the spirit world, you'd have to be "dead", since only the dead can roam the land. This means you can't take any totem of undyings, making the world a bit more challenging and would offer a unique gameplay rule in late-game Minecraft. This would also give more use to the newly added "Recovery Compass", since it's far easier to die in here. There would be typical overworld biomes with a gameplay twist to them, such as the Sunken Savannahs or the Deteriorating Desert.