I'm not sure what spoiler policy is for Mistborn, so I'm just gonna say that this has MAJOR Mistborn spoilers.
Each Shard on Scadrial has 2 things associated to itself: a Metallic Art and a Godmetal (I'm gonna capitalize this because why not). Hemalurgy for Ruin, Allomancy for Preservation.
It's fairly easy to demonstrate why Feruchemy is associated with Harmony (if you want me to explain, post Explain in the comments please because I don't have much time now)
For me, Godmetals have the most powerful effect in the Metallic Art of the Shard is associated with: Lerasium makes you into the most powerful Allomancer you can be, a Mistborn. For this reason, I think the info we have about H-Atium is downplayed (I have a theory, but again, I don't have much time so post Theory down below).
So, by the same logic, Harmonium/Ettmetal should do something really cool in Feruchemy. My theory is that we saw it in BoM. That's right, the primer cube.
My theory is that a Feruchemist filling a Harmoniummind would somehow dampen nearby Allomantic charges of a certain metal. Like tin, you would have to use a different metalmind per Allomantic metal. Then, tapping the metalmind would replicate Allomancy, centered on the Feruchemist. Tapping it faster coyld even replicate duralumin.
I think that harmonium alloys would enable you to store only Allomantic pulses of that metal.
This would mean that the Southern Scadrians have discovered how to mechamize Feruchemy, which is an idea I like very much because of all the possible uses, of which I'll be happy to tell you about at length, but not now.
Thoughts?