https://www.planetminecraft.com/data-pack/incendium-nether-expansion/
(some of desc copied from datapack page)
Incendium is a datapack made to completely revamp the Nether, beyond what has already been done by the Nether Update.
It is also completely compatable with BYG so i feel like it wont cause many issues but thats up to u guys
I really think this would fit the nether in E6 as the End and Overworld feel more finished and have more structures in the 4.0 update

Do you have a link to the datapack?

Oop so sorry here it is i edited the original post

Looks like the castle is an extra structure and doesnt replace fortresses or anything... I don't know that it would be any more crazy than the giant dungeon crawlers dungeons in the overworld... But I'd have to see it in game first

It is a shame that the biomes are included with the structures, it wouldve been better if the structures were a standalone thing

I think this is too much for Enigmatica tbh, we already have plenty going on in worldgen.

May i also add that they have a standalone datapack of the Nether castle structure
https://www.planetminecraft.com/data-pack/nether-castles-standalone/

Planet Minecraft

Nether Castles [Standalone] Minecraft Data Pack

Please join my Discord if you have any questions or if you want to discuss the pack! This pack is derived from Incendium. Please check out that pack if...

Looks pretty sweet... I might look at it tonight if I can pull myself away from actually playing the pack haha

I looked at it when looking at possible datapacks but incendium itself looks extremely big and probably a bit out of scope for our pack imo. The castles are cool but I worry about those being a bit too much too