First of all, thank you so much for the feedback! You are 100% correct, and this was definitely an oversight on my part.
In the last update, I implemented an automatic script to inject "Dark Essence" into all custom recipes. However, I forgot that this would also apply to the basic Abyssal Plate recipe (smelting category). Because of this, it started requiring both Abyssal Ore and Dark Essence.
Since standard furnaces in Factorio only have a single input slot, it became physically impossible to craft them in Nauvis, creating an unintended soft-lock.
I just released version 0.9.1 which fixes this. The script now correctly ignores smelting and metallurgy recipes. The Abyssal Plate now only requires Abyssal Ore again, allowing you to melt them freely in Nauvis right from the start.
Thanks again for pointing this out, and I hope you enjoy the rest of the mod! Let me know if you run into any other issues.