I’ve done and spec’d a fair amount of blackened steel for architectural metal work. The process is very similar to the video but we finish it with a black wax. We use this for interior spaces only. Even with wax it will rust fairly quickly in an exterior environment. I am a little suspicious that a coat of WD-40 like the video mentions will provide long term rust protection for an automotive application unless it’s for a heated garage queen.
I too would like to know more about the electroplating setup.