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I did have the thought of the Night connection, but the name Dustmother - as well as the several notable mentions of dust in-text above - don't seem to connect in any way to the concept of Night, while having a much closer connection to Stone (although I will concede that dust can also be dead skin or soil and not necessarily rock). It is possible they were both formed by Cultivation before Chemoarish was Unmade or maybe are a combination of two of the Old Magics (Stone and Night) if that's something that can happen. However them being created by Cultivation goes against another of my theories that all of the Unmade were originally formed by Honor before being unmade by Odium, with 9 Unmade + the Stormfather = 10 (Honor's number) - and potentially being what the Stormfather was referring to when he said "Our shame." in the latest chapter. It very well could be as simple as the Nightwatcher being the only other Spren of that magnitude that any normal person would have seen, or both taking the form of a mist/dust cloud when interacting with people - although I see where you're coming from, Sanderson does love his multi-layer foreshadowing.

From reading the Coppermind it seems that Aimia's weather and ecosystem was protected by fabrials, and the 'scouring' was an invading force destroying these fabrials and presumably killing many of the inhabitants. This implies that Dai-Gonarthis may have some ability to either control, support, or suppress large groups of people if he was part of this, and not necessarily any physical abilities. If it is Cusicesh or similar DG may simply have the ability to depress or subjugate the population. Spoilers for a WaT Szeth flashback chapter that was read by Brandon a while ago (let me know if this isn't allowed): Regardless of this it is certainly interesting that DG seems to be the only Unmade we know about with a direct connection to water as an element. We now know that Wind, Night, and Stone were all Old Magic and I think its pretty likely that the Unmade were derived from them just like the Stormfather, Sibling, etc. (Midnight mother being the most obvious example). Therefore DG is pretty strong evidence of at least one more of these Old Magic gods existing. I wonder how many there will be, it seems like something Brandon may want to keep up his sleeve until the second half.

The Unmade (or at least one of the Unmade) in Shinovar is going to be Chemoarish - the Dustmother. Evidence - Hessi's Mythica, Oathbringer Chapter 108 Epigraph Chemoarish is considered the mother of Dust. She is also either physically or mythologically similar to one of the Spren derived from the Old Magic, implying that they may have been similar (a Spren derived from Stone like the Nightwatcher was derived from Night) before her corruption. Dust can also be made specifically of small bits of rock. - The Way of Kings, Wind and Truth Chapter 22 Epigraph This passage appears at the start of the chapter and section where Szeth tells Kaladin about an Unmade being present in Shinovar. Dustbringers are one of the ten orders of Knights Radiant. They apparently have the ability to destroy large swaths of land, but they focus on control and mastery. If the Dustmother is connected to these powers of Division (and potentially Abrasion), just as the Midnight Mother appeared to be connected to Illumination and Transformation, then she may be able to cause similar mass destruction. Prior to moving to Shinovar, she may have resided in Bavland. It is known to be very dusty and barren - potentially caused by the Dustmother. They also curse by Chemoarish's name, implying they have more knowledge/myth about her than other areas. The Dustmother will be the Unmade inhabiting Shinovar. It is both culturally relevant as a Stone spren and also opposite to the otherwise green vibe of the area, meaning its effects may be more pronounced than elsewhere on Roshar. It is also one of the few Unmade with almost no information about them so far, and Brandon likely wouldn't reuse a previous Unmade. - Death Rattle This death rattle could be interpreted as being from the perspective of Szeth as a child, seeing the effect of the Unmade before leaving. Note that it specifically talks about dust. I may be wrong about it already causing destruction in Shinovar, as the locals "embraced it", but I think its likely that it will appear in the book in Shinovar. (BONUS THEORY: Dai-Gonarthis is also in Shinovar, relating to the "waters surged beneath" part of the Death Rattle (as the Black FIsher) and also being related to the sorrow of the child in the Death Rattle ("... holds my sorrow" is one of the few quotes we have about him)).

I actually had that thought at some point when I was creating this theory, but I couldn't quite make it work at the time. Now that I remember the Nightwatcher is directly related to the others, with some shuffling around that there are an even ten (if I'm not forgetting another Spren - and assuming the Stormfather isn't part of the Old Magic) - I didn't really have a Unmade that matched the Edgedancers, so the Nightwatcher would be a great candidate. However, it would adjust the theory to the Surges being split by a combination of Honor and Cultivation and I'm not sure if this is supported by the text. Also I think there is enough evidence to suggest that Tension is somehow important to Bondsmith's Connection powers (its their primary Surge on the chart - which seems to have a pattern of having an untapped ability with both Kaladin and Shallan, Adhesion doesn't appear to have any affect on Connection with the Windrunners, it would be kinda random to make it one of the Bondsmiths abilities if it had no additional use) - so it wouldn't be impossible for Ba-Ado-Mishram to be the Tension Spren imo. I think with current knowledge, both of these theories have about as much weight as the other.

Thanks for the detailed feedback! I still think there are too many connections for my theory to be completely debunked, such as Sja-anat's connection to the Mistspren, Chemoarish's connection to the Dustbringers through one of its names, regular mentions of rocks being important even outside of Shinovarian culture (My original statement wasn't meant to suggest that Shin are the only ones who worship rocks, but thematically I would imagine that a rock related Spren would appear in Shinovar - there would be quite a lot of setup for it in-text), etc. Somehow I already forgot that Wit referred to the Wind as Old Magic, so thanks for reminding me. However, I think the quote from Wit allows my theory to be mostly true with some adjustments. Just as Cultivation managed to create/extract the Nightwatcher from the Old Magic, perhaps Honor extracted the pre-unmade Unmade and Wind to govern over the surges. Surges existed in an unrestricted state on Ashyn, potentially allowing anyone to use any Surge (I don't know if there is confirmation they could specifically do this). I believe in Rhythm of War it is mentioned that Honor restricted the surges in some way when the humans went to Roshar, so it is possible that Surges were of the Old Magic and Honor split it to divide the powers - thereby creating 10 Spren. This may also explain how Honor ended up weaker than the other Shards - as well as potentially weakening himself to protect the Wind. This is getting pretty theoretical, so I'll leave it here.

Kind of cross-posting from the Reddit because I wasn't sure which place would be better (sorry if that's frowned upon). I'm not too up-to-date with theories - and haven't reread in a while - so forgive me if someone else has made these connections before or they've been debunked. This theory includes references to what I think may be major events in Book 5. Anyway, here we go: Originally, all Unmade were part of 10 'Elemental' Spren of Roshar with connections to each of the Surges respectively. When Odium came to Roshar, he successfully 'unmade' 9 of them into the Corrupted/Void versions, but was unable to unmake the 10th Spren, the Wind/Adhesion. This was because it was the most Connected to Honor ("The winds are of Honor" - Oathbringer) and is the reason that Voidbringers don't have Adhesion - because corrupting the Surgespren allows for that surge to be used by them. I believe that Sja-anat is the Spren of Truth as her unmade power seems closest to a form of spiritual Progression (regrowth) which is one of the Truthwatcher surges. Her perspective also aligns with being the element of Truth (Taker of Secrets, Englightening, etc.). She also seems to be able to corrupt Mistspren easier or they have an affinity with her as they are the only of her 'greater children' seen iirc - apart from Oathgate spren. She is also only visible as a reflection of light in the Physical Realm, the exact same appearance as a Mistspren. She may also be close to Cultivation as she shares her surge with one of the Cultivationspren's surges. This may explain her opposition to Odium and indirect alliance with Surgebinders, as she could be either working directly with or be aligned with Cultivation. There is strong evidence of the significance of Rock/Stone in the books (Shinovar/Szeth's worship of it, rejected book 5 title, Ryshadium hooves, Herdazian nails, Horneater teeth, etc.) - meaning that there are at least 3 major 'elemental' forces that coincidentally align with the Radiant Order names. The Spren of Stone is probably Dai-Gonarthis as we are yet to find out its abilities, but there are references to it 'scouring Amia' (earthquakes?), aligning with what has been hinted is happening/about to happen in Shinovar, a place that worships Rock/Stone. Finally, we know that Ba-Ado-Mishram has some power over Connection, indicating a relation to Bondsmiths and Tension (that likely somehow enables the Bondsmith power over Connection, otherwise Windrunners would also be able to influence it in the same way). Re-Shephir has obvious relation to Transformation and Midnight Essence (which may count as a core element), and Moelach has future sight which has only been seen to be possible through corrupted Illumination (Renarin). Chemoarish is referred to as the Dustmother - a pretty clear connection to the Dustbringers and possibly Dust as an element. Bonus super loose connections: Glys appears as a snowflake, so maybe Truth is just the ideal of Sja-anat, while Snow is the manifestation (making Truth literally a main part of the cover of book 5)? The Skybreakers/Gravitation could be related to Ashertmarn as they essentially embody a disregard for/corruption of law. I would a make a chart for this, but there are too many gaps both in terms of elements and a few of the Unmade. If you have any more evidence/theories/confirmations connecting to this, anything that disproves any part of it, or any questions, let me know!