Happy to start!
Dragnipur & Draconus
We have already seen the cart, but I don't think it will we have a larger role to play in Walk in Shadow. I wouldn't be surprised if we've already seen all of Draconus in Kharkanas Trilogy. And even if he reappears, we won't learn how he got chained. There's still A LOT of story to be told before the Tiste invasion on Wu, and AFAIR from Reaper's Gale intro, Anomander does not wield Dragnipur yet during the invasion. Maybe after Mother Dark turns from the Andii (because of Eleint blood?) she returns to Elemental Darkness to Draconus and then he creates the sword?
There is this quote from Midnight Tides, it's by Fear Sengar though, so likely unreliable as we know Edur mythology to be twisted:
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I imagine this to be a possible timeline:
1. Draconus retreats to Elemental Darkness (end of FoL)
2. Civil war is reignited (Huun Raal? Osserc's comeback?)
3. Tiste awaken to their draconic blood or drink Eleint blood
4. MD turns on them
5. Sundering of Emulrahn occurs and somehow pushes Tiste to flee to Wu
6. K'Chain unleash Kaschan ritual against Darkness-aspected sorcery to protect themselves from Tiste magic during the invasion
7. The ritual lets Chaos breach Elemental Darkness, Draconus puts the cart in motion to give MD a way to flee
Errastas & Sechul Lath
I looked at the Tor re-read of RG and the fragment with Gothos mentioning Kilmandaros' children losing her way caught my attention. We know that Sechul Lath is her son and Errastas is his brother, though they only share the father IIRC. We know from K'rul in FoL that Errastas plans to abuse the warrens, so maybe the sundering of Emurlahn was their deed? There was also some speculation that Kilmanadaros might be Icarium's mother and we know that he 'wounded' Emurlahn, so maybe Errastas and Sechul somehow used Icarium to destroy Emurlahn? It's a long shot, but would also explain why Gothos, a suicidal recluse, was there to intervene - some sense of responsibility for Icarium's deeds?
Also, Gothos lives nearby an Azath house that will in the future be in Letheras and it is still to welcome Silchas and Sheltatha Lore to its loving embrace. We know from Toll the Hounds that Gothos knows about Builders and exploits their power. He seems already aware of them in FoL:
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‘Builder?’
‘The ones who make Azath Houses.’
So Gothos might have a bigger role to play in the Wu invasion than we were shown in MT and RG.
High King
I think the humans are already in this world. There's this tidbit from Raest about the War on Death:
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'Petty tyrants' are the only race not named. It might just be Erikson toying with us and avoiding saying it out loud: Kallor is already leading a human empire.
Also, I think we get foreshadowing of Ereko's death from Hood and a Thel Akai woman Erekol:
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‘Aboard a stout ship.’
‘In what sea?’
‘West. They ply the Furrow Strait, hunting dhenrabi.’
‘Near the High King’s lands, then.’
She shrugged. ‘Thel Akai fear no one.’
‘Unwise. The High King has set his protection upon the dhenrabi, and their breeding waters.’
‘My son is safe. What matters it to you, Hood?’
+
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‘I see him in the High King’s shadow. That is not a good place to be.’
Quick Ben
Okay, so after FoL it's not anymore a question of if but how Korya Delath becomes Quick Ben. She's a mahybe, aspected to Darkness, trained to prolong her life by absorbing souls. And she's a counter against Errastas, which is interesting.
Haut gives Korya a finnest at some point and there might be a hint in that. Maybe when she collects a number of souls she can absorb, she locks her power in a finnest and then passes it on to the next mahybe and so it goes for millenia?
Edgewalker
I think it's Yedan Narad. One of the first Edur, possibly the first Watch. He is's supposed to protect the shoreline (Emurlahn in Shake!) and can see the destiny of a future Yedan. He also swears to answer Anomander's call shall he make one, and we know that both Anomander and Edgewalker will be instrumental in protecting the Throne of Shadow. And in RG intro Anomander seems to know whereabouts of Edgewalker ('Edgewalker is committed elsewhere').
Anomander's mother
That's the craziest one, so I left for the end. That's what Caladan tells Anomander:
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‘Rake?’
‘Purake is an Azathanai word,’ Brood said. ‘You did not know? It was an honorific granted to your family, to your father in his youth.’
‘Why? How did he earn it?’
The Azathanai shrugged. ‘K’rul gave it. He did not share his reasons. Or, rather, “she”, as K’rul is wont to change his mind’s way of thinking, and so assumes a woman’s guise every few centuries. He is now a man, but back then he was a woman.’
Much later, Skillen Droe meets with K'rul at the Sidleways:
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‘My days of birthing are done, for a time.’
‘But not, it seems, your bleeding.’
It's not said outright, but strongly implies that K'rul has children. What if he/she was the mother of Anomander and his brothers? Being half-Azathanai might explain why Anomander and Silchas partially defied the Mother Dark's blessing of turning black.