Let’s assume a Feruchemist has access to some other form of Investiture, maybe with a Perpendicularity, liquid Dor, becoming a Radiant, getting Breaths, or maybe even tapping Connection to become Elantrian or something. We’ve seen from TLM that Allomancers can use Investiture from a Perpendicularity instead of metals, so can Feruchemists do the same? If so, how would something like a coppermind work, where the attribute has data stored rather than just an amount? There’s probably a WoB explaining this somewhere, but I can’t find it.
I’m actually not sure we have any information on this. A feruchemist sort of requires a metalmind, and I am not entirely sure they can substitute other Investiture as a metalmind or not. This is a really interesting question and perhaps it should be brought up to Brandon at the next spoiler stream or livestream Q&A.