Plastic Misting

It wouldn't work at all, pacing-wise. The only reason why it works for Game of Thrones is because there are so many separate stories with so many mini cliff hangers. They could just slice up the plot so some story arcs have a slow part while an other story arc has a climax or a cliffhanger in the same episode. This wouldn't work with Mistborn.

I didn't really like it. Imo it just tried way too hard to be dark, to the point where some scenes were just ridiculous. And there were so many dumb scenes of self doubt. "Oh no, I'm so ugly, I don't deserve to be with you!" "Oh, I'm such an evil killer, I don't deserve to be with you!" Especially pointless since you already know that forced conflicts like this one always resolve in the end. And the silly names, Wetboy and Mama K. I couldn't get into it, no more suspension of disbelief and everything was ruined.

It could also be something about his father's chalk, assuming he had it on him at the time. Doesn't seem likely, but noone mentioned it so far.

It seems very likely that it has some connection to his wife. I'm assuming that once we get to the book with Dalinar flashbacks his entire past will be clear. Therefor all unknown elements of his past have to fit into one continuous story. His wife died and then he went to the Nightwatcher. Another thing to note is that it's the old Dalinar who got his boon. The killing and drinking Dalinar.

I think it has to do something with a sort of magic we haven't seen yet. Either he must've known Dalinar would fall asleep at that very moment or he used some sort of sleeping spell. And even if Dalinar was just sleeping, prying a rock out of ornament and writing on a wall with it makes quite a bit of noise. From this and the other arguments ITT I believe we can exclude Szeth as a suspect. Dalinar seems the best fit. If it had been somebody else we would've had more clues. He also tells Kaladin that he shouldn't worry about how the writer got in. Considering he is worried about assassins I can't see any other scenario where this behaviour makes sense.