I have played this mod at some point with friends using the 1.19 datapack available on planet Minecraft as part of a quick custom-made fabric modpack (the same one with regions unexplored)

What is it ?

Bastion Overhaul is a datapack for 1.20.1 (doesn't seem to work in post 1.21+ versions, but you can still try) which aims at reworking bastions ;
It aims at turning the remnants back into their prime , changing them from lava-filled ruins to dangerous piglin-filled strongholds.

What does it offer ?

Entirely-reworked bastions from the ground up, with more piglin brutes/armored piglins within much prettier structures, each variant was rethought, effectively integrating 1.18+ blocks and changing platforming from being the main challenge back to combat instead.
There isn't much to add as it does what you expect it to, changing the bastions into an interpretation of their original brutalist past form while making them harder to beat but more rewarding;

However I have noticed that it seems some of the mobs added to the structures have not their spawn set to be persistent , which leads to some despawning if you get too far after the structure generates;
It also seems that some worldgen elements do not get removed when the structure spawns in their place, leading to piglins sometimes dying of suffocation before you get there; I have not seen it happen often but I would rather warn.

In conclusion

This datapack while certainly not the only one to add nether features and structures, is yet one of the sole way I have found to actually upgrade the vanilla bastions instead of adding whole new structures (Others on this specific list may include the datapack Incendium , which among adding new biomes makes it so bastions generated in their custom biomes get transformed into custom forms, which look nothing like the originals except for the hidden bastion in basalt deltas which looks really pretty and is really challenging)
I know this datapack works well with some nether Worldgen mods ( Scorching Nether integrates surprisingly well with this one, and I might have played this mod a while ago with Regions Unexplored on the side) but due to it changing the vanilla bastions I wouldn't be surprised if it gets incompatible with larger-scale nether-remodelling mods; It's a case by case scenario where you will have to test things out if you're thinking of adding it to your modpack .
This person has also made other structure reworks such as Ancient city and Trail ruins ones (which I like less for various reasons).

Really good, but definitely has flaws which are waiting to be fixed.