Nether has 16,000 nodes in the game. This might be too much but it was used to shorten the distance of realms and and more realms from 0-16,000 whereas nether is 16000 to 32000 (negative depth of course).
Ive been considering trying to add caverealms back in and maybe reducing nether again. Check out the underworld in df_caverns in singleplayer. Maybe just reducing nether and leaving "Hell" as a very deep bottom/core of the earth biome would make sense. I would like to learn more about biome registration too to maybe we can create biomes in the future too.
Either way, for now lets look into adding stuff into the nether. I was using the game doom as a base inspiration for nether mobs but they dont show up often . Nether is too dark too. Too plain. Needs variety like minecraft added. Maybe we can talk about this on the nether forum in the minetest forum and everyone in the greater MT community could benefit here too?