The Lord Ruler

It's Preservation and Ruin,which both change hands on-screen(on-paper?).

It may seem like a big stretch, but it took Rashek exactly 16 days to reach the Well of Ascension, exactly sixteen percent of populations were getting the mist-sickness in the Hero of Ages, and they all were sick for exactly sixteen days, and they were snapped afterwards, and could burn metals. On top of all of this, in the passages before chapters, it's mentioned that by Sazed that Preservation used the number 16 as a sort of signature. And Feruchemy is based on Allomanic metals because it's a mix of Ruin and Preservation's magic systems, and uses those to operate. As for Roshar, the Knights Radiant and the Heralds are both related to Honor, and we haven't really seen much of the other Rosharan shards.

But Lerasium Mistings wouldn't work, because once a person swallows the Lerasium, he/she becomes a Mistborn. Or does this not work with Mistings?

Mild Mistborn spoilers, I guess. The number '16' is everywhere Perservation is: 16 allomantic metals, 16 years before the people Preservation chooses reach the Well of Ascenscion, and tons of other stuff I don't remember. Likewise, the number 10 is everywhere on Roshar: 10 heralds, 10 of the cities that are constantly mentioned, 10 orders of Knights Radiant, and so on and so forth. There are 16 shards, right? Maybe these numbers have something to do with ranking or which piece separated from Adonalsium first.

This makes sense, especially if their body just keep getting reused. After all, don't the bridgemen just assume that the corpses in the chasms get washed away by highstorm floods? What if they just come back to life and walk away?