I think I was sold on Sanderson fully after reading Alloy of Law and being so impressed with the way he could swivel a fantasy world into a whole new genre of western/fantasy mix. I'm really, really hoping he'll stay with his initial plan of the next Mistborn era being a sort of 1980s political...
He has both allomantic and feruchemical spikes so he's able to store age much the same way that the Lord Ruler did, and he has the bag of atium he kept from the Kandra that tried to sell it. So he's nearly immortal.
I'd think it would still have to be, surely. Even though there's some sense in which the two shards are opposing forces, they still form a single shard entity now, Harmony, which over time must gradually bend Sazed's personality to this new Intent. Though hopefully that will often work out for...
Khriss doesn't appear in Stormlight but she has a cameo scene in the Wax & Wayne trilogy.
She's the author of all the Ars Arcana sections at the ends of the books, and Sanderson has said she's probably the most comprehensively knowledgeable person in the Cosmere, even more than Hoid.
Kassina, re: the Sanderson annotation......while there isn't an instance of joyful Snapping in Mistborn so far, in the Stormlight books there is a similar moment when magic becomes accessible for people, where in a later book in the series it's implied that at least one character became magical...