Many people have postulated that it is Shaeonanra speaking through the Mutilated, based on extratextual remarks from the author, as well as hints in the text, such as the speaking in rounds, or the line "the truth spoke with one soul" [paraphrased].

Likewise it has been suggested that the Consult created the Dûnyain, or directed them to Ishual. The biggest difficulty that this theory faces is the fact that the Consult clearly do not know who the Dûnyain are, as seen in the epilogue of TWP, and elsewhere throughout PoN. There are a few way around this, though, and in this post I will present a new explanation for how it could be the Consult do not know who and what the Dûnyain are.

The first explanation is simply that they forgot. We know that you can't raise walls against what is forgotten, and with 3/4 of the Consult leadership being ancient, all it takes is for Shae to become a bit erratic and the whole endeavour falls from memory.
The other possibility is that Shaeonanra set this up in secret, paranoid that his inhuman allies had no need of soul trapping devices, and could choose to deny him the means to keep his soul in the Inward if he displeased them. We only know for certain that Aurang (and possibly Aurax) has no knowledge of the Dûnyain.

These two explanations seem unlikely, though. The problem with the first idea is that the Inchoroi seem to have decent enough memory, so an undertaking such as this would probably not be easily forgotten, and the second falls apart because Shauriatas appears to be on good terms with the rest of the Consult, and they seem to need him as much as he needs them.

My idea is if the Consult has something to do with founding the Dûnyain (far from certain, to say the least) that it was another member of the Mangaecca, not Shae, who set them up. We know that by the First Apocalypse Shae was using his soul trapping larval thing, and that other members of the Mangaecca were able to hold on for an unnatural length of time, but were all dead by round 2. Though Shae might have a privileged position amongst the Consult, there is nothing to say his brothers enjoyed such security.
But if that schoolman should die before his breeding project bore fruit, all knowledge of Ishual would leave the world.

That is correct. In classic Overlook fashion, they were inconsistent. TTT does not have "First Edition" printed on the publisher page, unlike the others. Also, AFAIK Overlook only ever did 1 printing of TTT in hardback.

Concerning superficially similar sex organs, I assume something going on like with the spotted hyena: females have a "pseudo-penis" so they appear to be male, but there is still sexual reproduction.

But why is Sil's shield so big? Are you suggesting that the shield is a relic from the days when the Inchoroi were huge, but the Heron Spear is more recent (or was shrunk down from a previously bigger weapon)?
That still doesn't explain how Aurang was able to wrestle the Tall and win.

Maybe just that the Tall have grown, substantially, by the time we see them? A Tall at Arkfall was 2-3 meters, whereas in TUC they are like 5?

I don't think anything in the text contradicts the idea that it is a lot larger than we assume: it was stolen by Seswatha and Nau-Cayûti together -- perhaps this is the reason Seswatha needed Nau-Cayûti to come with him -- and was transported in Anaxophus' chariot, so it could actually be ~20 ft long.

The exact dimensions are never really given, so yes it could be any/all explanations.

Then again there is nothing to contradict the idea of the spear being like a laser pointer, other than the fact that it is a silly image.

This provides the primary drawback of the type of obfuscation Bakker loves - you can end up in weird places, like a fearsome weapon being a toothpick.

We know that there are ten times as many Sranc roaming the Ancient North today as there were during the First Apocalypse. Yet Sranc are always depicted as male, so would appear to be incapable of mating with one-another.

There is also a Sranc who says, in reference to the Old Fathers: "Father… father! We have no fathers save the earth!", which suggests the Sranc somehow gestate within the earth (like Orks!), but I seem to remember somebody mentioning a reference to female Sranc, so perhaps that is wrong.

It is possible that all Sranc spill out from Golgotterath, but if that is the case how are there wild Sranc clans who don't even know who the Inchoroi are?