HotAsDaySide

I think the mists in Era 2 are nothing super invested anymore. Sazed needs all the power of Preservation to keep Ruin's power in check so it wouldn't make sense to put Preservation's power back into the mists, as was the case in Era 1. The mists could then be of Ruin but that doesn't seem too logical: there's nothing destructive in the mists; in fact, Era 2 mists don't do much to begin with. If the mists were more of Ruin, they would be much more similar to the Deepness but that's not the case. Instead the mists are just an occasional misty night without any (canon) powers. There's also the thing that the Era 1 mists were Preservation's pure power without (much of) a consciousness directing it. In Era 2, Harmony has strict control over both shards so he'd probably put the excess power to a use instead of having it floating around freely. When Wax had access to them wass probably more due to Harmony's special attention through the spiked earring than anything else.

I've seen the future of the Cosmere and it is bright...

I personally don't think this is likely but who knows what could happen. After all, Shallan's different personalities/disguises show different preferences. Shallan's love/fondness for Kaladin is very apparent in Veil, her love for Adolin is mostly connected to Shallan. Brightness Radiant is the personality Shallan uses when she wants to be professional in her capacity as a Knight Radiant. This personality echoes Jasnah a bit in my opinion so maybe... Plot twists are Branderson's specialty, are they not?

I love this theory. I totally see Brandon foreshadowing something like this with his allomantic and feruchemic tables. I don't know if you've read Oathbringer already so mild spoiler ahead. Other than pointing this out, I'm afraid I can't offer no more insights. I'm a bit too new for that, I'm afraid.