In this story, there are a couple references to a stranger with a hat:
Men like these, though ... they’d probably take less than an hour to violate one of the Simple Rules and bring the shades upon them. Daggon put the idiots out of his mind. That fellow in the corner, though ... dressed all in brown, still wearing his hat despite being indoors. That fellow looked truly dangerous. I wonder if it’s him, Daggon thought. So far as he knew, nobody had ever seen the White Fox and lived.
“It’s the man with the long neck, isn’t it?” William Ann asked. “I remember his face from one of the bounties.” “That’s just Lamentation Winebare, a petty horse thief. He’s barely worth two measures of silver.” “Who, then? The man in the back, with the hat?” Silence shook her head, finding a sequence of pages at the bottom of her pile.
I'm guessing this could be a Cosmere world-hopper. Has there been any mention by Sanderson or educated guesses as to who this might be? Hoid is kindof the go-to guess. I know he disguises himself, but this description doesn't sound to me like Hoid. At a glance it doesn't have some of the Hoid-like themes (story-telling, jestering, beggars, travelers, etc). But all we really get here is a brief glance. Perhaps Nazh, since he is a Threnodite? I'm not sure if a description of him has been offered anywhere.