Which Arcanum Unbounded story is important for The Lost Metal?

On the thread for questions for the Halloween Stream Brandon said twice that there is a non Mistborn story in Arcanum Unbounded that is relevant for the Lost Metal [https://www.reddit.com/r/Sanderson/comments/yihn1v/comment/iulmbcj/?context=10000](https://www.reddit.com/r/Sanderson/comments/yihn1v/comment/iulmbcj/?context=10000) , [https://www.reddit.com/r/Sanderson/comments/yihn1v/comment/iulm61x/?context=10000](https://www.reddit.com/r/Sanderson/comments/yihn1v/comment/iulm61x/?context=10000) )

Sixth of the Dusk is set in the Future, so it can be eliminated.

I don't really see a way for any of the SfSitFoH characters to become Worldhoppers, the only way I can see a SfSitFoH Crossover is if the Scadrian Subastral ends up being Invaded by Shades from the Threnody Subastral.

If a Stormlight Character were to appear in TLM, it wouldn't be Lift, but I think there is a small chance that we might have an appearance of Arclomedarian, the Sleepless Lift meets in Tashikk.

While White Sand has a good chance of being important for the Lost Metal if Trell is Autonomy, the White Sand excerpt in Arcanum Unbounded is not a lot, and if it is relevant, then the rest of White Sand would also be relevant.

The same goes for the Hope of Elantris.

This leaves the Emperor's Soul, but the Problem with it is that Shai (assuming she is the Crossover) shouldn't be able to perform Forgery outside of Sel. There are of course ways to get around this. What also speaks for Shai is that Brandon has said multiple times that Shai will make appearances in other books. ([https://wob.coppermind.net/adv\_search/?query=Shai](https://wob.coppermind.net/adv_search/?query=Shai) )

So, my bet is on Shai, having joined a Cosmere spanning Organisation, hunting for the Imperial Fool (Hoid), and missing him closely time and time again throughout the Lost Metal. She might have joined the 17th Shard, whose members already are hunting for Hoid.