Dear lord, by the time it comes October, we'll have figured out the whole book. Or, at the very least, come up with some very convincing theories that sound good enough to be in the book.
I like where this is going. Mists used for Allomancy, and Ruin and Preservation acting through it? That's brilliant. And if Vin's experience has taught us anything, it's that you can use the mists for Allomancy. The triad of magic systems interacting with the mists (and Feruchemy not caring either way), also brilliant. Now we are on the right track: discussing how Ruin/Preservation are related to the magics. Very good indeed.
There's an interesting correlation, though. Feruchemy, perhaps, does not affect the mists because it existed before the Ascension. The Worldbringers stored their prophecies in metalminds. However, Allomancers didn't exist before the Ascension at all. If Hemalurgy is like some opposite Allomancy, or something, it could be a logical conclusion that Hemalurgists, whatever they may be, did not exist before the Ascension, either.
Yet the mists did exist before the Ascension, or at least it is heavily implied/theorized that they did. Perhaps Allomancy is somehow derived from the mists, which would mean that it is derived by either Ruin or Preservation.