Forgive me if someone else posted this theory - a few google's did not resolve anything.
I just finished listening to the graphic audio book rendition of Stormlight, this time going through the series in the light of the obviously (imho correct) theory that Chanarach is Shallan's mother. Given the prologue, it's pretty clear that Chanarach will be part of Stormlight 5.
But then my inner Kelsier got going. There is always another secret. Chanarach being Shallan's mother is far more obvious than usual fantasy secrets. Maybe it's not so much the secret as the secret that hides the real secret.
Here's my theory. Not only is Chanarach Shallan's mother - Shallan is well aware that Chanarach is a herald, is alive, communicated with her on Braize \_after\_ her death, perhaps robbed Jasnah at Chanarach's bidding and did something that resulted in Chanarach "breaking" and returning to Roshar, thus starting the true desolation.
From the best chapter that Brandon has ever written (at least to me) "Red Carpet, once White"
Sanderson writes in third person limited. Theoretically, the narrator can only narrate something that Shallan knows or feels. Quite often, the narrator is thinking back to some event in the past and, therefore, "knows" something that the character knows or feels in the present and can, therefore, bring it up in the context of a a flashback or memory.
Of course, we are led to assume that Shallan feels this way metaphorically—that it is because she just offed her mother. If we are really into things, we may suspect that Shallan feels this way because she sent someone into Braize. But maybe, just maybe, Shallan's future knowledge is a step beyond that—she knows that her mother is a Herald, that she is currently in Braize, and that her return will spark a desolation.
How would she have this information? First it's possible to check up on the population of Braize:
Interesting word. Communicate. What's the Cosmere cellular plan? Oh yeah. Seons. Very very rare on Roshar. assuming it's not some other skill she randomly has - where would Raboniel get a Seon? How about that one and only distributor of Seons - Mraize. The same Mraize and the same ghostbloods that Lin Davar was involved with.
What better way to encourage Raboniel to meet with his babsk then to give her a mechanism to ask to meet with her babsk?
So there is a decent possibility that Raboniel communicated with Braize via a Seon.
Doesn't change that Seons are rare. So rare in fact, that Shallan has already run into two of them:
RoW Chapter 30:
We find out later that this Seon is special. It's a unbound Seon.
Okay, Shallan had a Seon as a child. Seons are useful. Also magical. And stored in cubes now. Let's see if there are other mentions of Shallan and cube like structures, say by a certain King's wit:
And there are more references:
Words of Radiance Chapter 61:
We've been assuming that it was Pattern in the safe, but this is a lie that Shallan tells herself (and a lie that Pattern repeats). It's explicitly a vision, not a flashback:
At best, it was never a pattern inside the strongbox; at best it would have been a testament. But a testament was a shardblade—a bonded shardblade. It would have disappeared and not remained in the strongbox. It can't be pattern, and it can't be a testament in the box.
It's pretty straightforward to assume that it was a Seon in the box, placed there after the Chana-kabob. So why does Shallan think that her mother's soul is in the box - Simply because Shallan sees or hears her mother in the Seon. Seon's make people's face appear, glowing (elantris, Chapter 2)
The monster is not Testament or Pattern - but rather Chana herself, communicating from Braize.
So, what would our intrepid do? Ignore the box once her father died, or use the box to communicate with her mother?
So this is my theory. Not only is Shallan using a Seon, she has used it in the past to communicate - with Chanarach.
From there you can can ask some interesting questions. Why is it that Radient and Veil only physically showed up after the desolation occured? Shallan's powers were manifesting (to some degree) between the period in which she broke the bond with Testament (which we don't fully understand) and before Pattern cut over to the Physical realm.
I think there is much more communication, and perhaps even open direction coming from Chanarach to Shallan. Shallan is, by definition, a unreliable narrator. Perhaps Shallan has been hiding Chanarach's role all along.
Finally, Veil was re-integrated into Shallan because the emotional event at the core of Veil's creation was resolved - her murder of her mother, and breaking of Testament's bond. Yet Radiant is still around - and Radiant is much more recent then Veil. Could it be that acknowledging that her mother is not dead (a fact she "knows") and that Shallan has perhaps been actively working with her mother resolve Radient? After all Radient looks just like Chanarach as well?