I'd like to spawn a Ruin at specifc co-ords in the nether upon overworld creation, but AFAIK there is no way to do it with the current commands. I've tried other mods (Pillar, Rec Complex, StructPro, WorldEdit) and Ruins is the only that handles the Stargate mod properly (doesn't try to copy the exact Stargate address and does copy the gate properly so it does work afterwards).

Any chance of adding this?

Thanks

Have you tried the readme?
https://github.com/AtomicStryker/atomicstrykers-minecraft-mods/blob/1.12.2/Ruins/src/main/resources/readme.txt