This theory was formulated based on my observations during the reread, as documented at http://greatlordofthedark.blogspot.ca

THE BORE IS IN TEL'ARAN'RHIOD

The importance of Tel’aran’rhiod to the story is such that I believe it is pivotal to the Last Battle. I have concluded that the Bore which Rand must seal is in Tel’aran’rhiod.

THE BORE IS NOT IN THE REAL WORLD

Demandred stands in the Pit of Doom and thinks: Physically, this place was no closer to the Bore than any other in the world, but here there was a thinness in the Pattern that allowed it to be sensed.

The Bore is equally distant from every place in the world.

WHERE ELSE THE BORE COULD BE

Verin explains the structure of the Pattern to Egwene: Let these [parallel lines] represent worlds that might exist if different choices had been made, if major turning points in the Pattern had gone another way: The Worlds reached by the Portal Stones. Some in the Age of Legends apparently believe that there were still other worlds – even harder to reach than the worlds of the Portal Stones, if that can be believed – lying like this [cross-hatching the first set of lines]. In all of these worlds, whatever their other variations, a few things are constant. One is that the Dark One is imprisoned in all of them.

In all of them? How can that be? Are you saying there is a Father of Lies for each world?

No, child. There is one Creator, who exists everywhere at once for all of these worlds. In the same way, there is only one Dark One, who also exists in all of these worlds at once. If he is freed from the prison the Creator made in one world, he is freed on all. So long as he is kept prisoner in one, he remains imprisoned on all.

The point is that there is a third constant besides the Creator and the Dark One. There is a world that lies within all these others, inside all of them at the same time. Or perhaps surrounding them. Writers in the Age of Legends called it Tel’aran’rhiod.

There is a simple way to remove the supposed paradox from Verin’s explanation. Place the Bore in the world that surrounds all the others; in Tel’aran’rhiod. One Dark One, in one Bore, for one Tel’aran’rhiod, in one Pattern.

This placement also explains how the Dark One can win in various Mirror worlds yet still be imprisoned. He is taking them down, one by one, until there is only Rand’s world left. No paradox!

I drew a map! (hyperlink included in case of image posting problems, but you can see it on my blog as well)

Simplified Cosmological Map of the Pattern in the Wheel of Time: link

HOW THE BORE WAS DRILLED IN TEL'ARAN'RHIOD

In the Age of Legends, two researchers, Mierin Eronaile and Beidomon, found a new source of Power that was not split like the One Power, but could be used by either sex. They drilled a hole in the Pattern to be able to touch this Power, and released the Dark One. Mierin later chose the name Lanfear. She claimed dominion over Tel’aran’rhiod because she was the pre-eminent Tel’aran’rhiod researcher of her time. The fact that it was Lanfear who drilled the Bore infers its connection to Tel’aran’rhiod.

In Tel’aran’rhiod, things can be done through sheer force of will. Things such as finding an elusive power source, and boring a hole to a place outside the Pattern. The Bore was drilled using the properties of Tel’aran’rhiod itself.

HOW TO SEAL THE BORE

Lews Therin was able to seal the Bore by precisely placing seven seals over it. Each seal had a real-world focal point made of cuendillar. The seals were not completely effective because they were only powered by the will of men; no women helped.

Cuendillar is unbreakable. But it could be broken in Tel’aran’rhiod, with enough will. Altering the nature of cuendillar is impossible without some reality-altering power. If the true seals are placed in Tel’aran’rhiod, over the Bore, and are subject to its rules, then any degradation in them caused by the Dark One’s force of will (or humanity’s lack of it) can affect the seals in the real world, causing unbreakable cuendillar to weaken and become brittle. The very name cuendillar, or heartstone, implies that its ability to resist damage comes from the heart, or from force of will.

Herid Fel gives Rand two pieces of advice to explain how to make effective seals. First, belief and order give strength. Have to clear rubble before you can build, meaning Lews Therin’s seals must be removed. Second, the Dark One’s prison must be whole again, not simply sealed. The One Power cannot do this alone, it must be done with force of will in Tel’aran’rhiod, and made permanent. It is known that this will take place at Shayol Ghul itself.

Shayol Ghul, the epicenter of the Dark One’s presence in the waking world, is a place where unreal weather exists and caverns can change shape; where reality is malleable in the Dark One’s hands. The unnatural Blight radiates outward from it. Just as if this place had the features of Tel’aran’rhiod and was an extension of it. The closer to Shayol Ghul, the more it is like Tel’aran’rhiod, and the more the immediate environment is under the Dark One’s command. Things can be done there that cannot be done anywhere else. Things could happen there that could happen nowhere else. Shayol Ghul has these properties and has a thinness in the Pattern because it is a place where a permanent similarity between the real world and its reflection in Tel’aran’rhiod was created, making a place where it is possible to simply step from one to the other. It is a place that has the malleability of Tel’aran’rhiod, and the permanence of the waking world. Tel’aran’rhiod spills over into the real world from this spot, altering reality outwardly as the Dark One desires, increasing the size of the Blight, for example, or giving Shayol Ghul and the Pit of Doom their unique properties.

From this spot where they overlap, this threshold between worlds where they are one and the same, the reality of the waking world can be shaped, and perhaps the Bore in Tel’aran’rhiod itself can be permanently sealed. Here, it is possible to will the Bore not to exist at all, as it was before, if done with sufficient willpower.

THE NATURE OF THE DARK ONE'S POWERS

With the Bore in Tel’aran’rhiod, it makes sense to consider if the Dark One’s powers can be explained by comparing them with what can be done in Tel’aran’rhiod. The Dark One alters reality, which is also a property of Tel’aran’rhiod.

Rand saw the drilling of the Bore in the glass columns of Rhuidean, and the destruction of the Sharom floating above the blue and silver domes of the Collam Daan, a prestigious research facility.

The drilling of this Bore had several symptoms. First, the ground and air rippled. A similar effect happens in Knife of Dreams from a bubble of evil, and again from the balescream in The Gathering Storm and Towers of Midnight. These are events where reality is being altered. Second, the Sharom burst apart in gouts of black fire. It broke apart like an egg and began to drift down, falling, an obsidian inferno. Third, darkness spread across the sky, swallowing the sun in unnatural light, as if the light of those flames was blackness. Unnatural events can be created in Tel’aran’rhiod or by the Dark One. The only known way to alter the reality of an environment is when it is done in Tel’aran’rhiod.

Bubbles of evil stemming from the Dark One can alter the reality of random places in the world, just as nightmares do in Tel’aran’rhiod. The effects of a bubble of evil would not be odd in Tel’aran’rhiod. All examples of bubbles of evil can be explained by the Dark One doing what is considered to be impossible; using Tel’aran’rhiod to affect the waking world.

Using the True Power granted by the Dark One allows one to create weaves with the same effects as those of the One Power, but which are undetectable. All True Power effects could be attributed to being able to use Tel’aran’rhiod properties, for example, to tear a hole in the Pattern for Traveling or creating balefire.

The Dark One’s luck, if it truly exists, can be explained by altering reality. Mat’s luck would come second in a contest where the results are not dependent on random chance but on the force of will of the participant.

Upon her release from the vacuole, Moghedien believes Moridin’s base of operations is near by Shayol Ghul, since the only other possibility she sees is that it lays in Tel’aran’rhiod. The strange ‘castle’ in which Moridin convenes the Forsaken has certain properties that are like Tel’aran’rhiod: They could as soon make shocklances or sho-wings as view-walls outside of this place, so close to Shayol Ghul. It was far from anywhere, in any way that most humans would understand.

When the Forsaken flee to escape Rand or trap him, even those with no apparent facility in Tel’aran’rhiod choose to go there. It is a place of ultimate safety for these cowards. They always take minimal risks, so when faced with destruction, they seek shelter in a place close by their lord and master, where his power and ability to aid them is strongest: Tel’aran’rhiod.

Transmigration of dead souls, who wait in Tel’aran’rhiod until their rebirth, is that much simpler to explain if the layer of the Pattern closest to the Dark One is Tel’aran’rhiod.

Entering Tel’aran’rhiod in the flesh is evil, but it is never explained why. The risk stems from the danger of being unmade or altered, such as Moghedien does to turn Birgitte into a child. The evil stems from getting used to having reality bend to your will, from beginning to believe that your desire is sufficient reason for a thing to exist in the way you imagine it.

CONCLUSION

Tel’aran’rhiod did not feature prominently as the setting for the final confrontation of the first 5 books, or in the most recent books, and in various other significant places throughout the series, only to be ignored in the Last Battle. All of the characteristics of Tel’aran’rhiod have been patiently held back so as not to give away the means by which Rand will defeat the Dark One. The Last Battle will not simply involve using powers and abilities, but can only be won by Rand choosing an identity and embracing it with all his will, in a place where thought becomes reality. When he stands at Shayol Ghul on the precipice between worlds, his sheer force of will, bolstered by humanity’s collective will, can repair the Dark One’s prison such that you would never know it had ever been bored into.