Lanfear drilled the Bore

Lanfear will be the key to Rand sealing the Bore and defeating the DO at TG. We know from the BWB that Lanfear, along with another AOL scientist named Beidomon, actually drilled the Bore. It therefore makes sense that she should know more about the Bore than anyone else and would be the most likely person to figure out how to seal it completely.

Lanfear already has a plan to defeat the DO.

Lanfear is the only Forsaken we've seen to actually defy the DO:

Her voice dropped to a whisper, equal parts eagerness and fear. "Two great sa'angreal were made just before the end, one that you can use, one that I can. Far greater than the sword. Their power is beyond imagining. With those, we could challenge even...the Great Lord himself. Even the Creator!"

-TSR Ch. 6, p. 189 (paperback)

Lanfear is not stupid. She knows what she'd be in for if she tried to overthrow the DO with Rand and lost. She wouldn't risk that unless she was absolutely sure she'd succeed. She wouldn't even suggest it to Rand unless she already had an idea, a plan as to how they could use the CKs to seal the Bore. And we know from WH that this was not just her spouting BS to Rand:

So he had found a woman to use the other access key. She would have faced the Great Lord--faced the Creator!--with him. She would have shared the power with him, let him rule the world at her side.

-WH Ch. 35, p. 641

She actually intended to go through with this plan.

Min's Vision

There was new evidence hidden in ACoS that Rand needs Lanfear. There were two thoughts from Min's POV:

What good to tell him he would almost certainly fail without a woman who was dead and gone?

-ACoS Ch. 35, p. 696 (paperback)

Min sighed regretfully, but it was not as if she had really expected Moiraine to turn up alive. Moiraine was the only viewing of hers that had ever failed.

-ACoS Ch. 35, p. 700 (paperback)

Many people assume that the first quote refers to Moiraine because of the second quote, just 4 pages later. But there is no evidence at all that the two viewings are connected. Min's vision that she thinks failed refers to her vision that Moiraine will marry Thom, which has absolutely nothing to do with her vision about Rand needing a woman dead and gone to win. Although never explicitly stated, there has been a plethora of evidence to this effect. Moiraine has several times expressed absolute confidence that Thom was still alive. She also told Thom in TSR that she was certain he'd survive his trip to Tanchico. There is also:

Finally she said, "I could wager I know the face of the man I will marry better than either of you knows that of your future husband."

-TSR Ch. 6, p. 126 (paperback)

and in her letter to Rand:

"You see, I do not know what happens in the world after, except perhaps for one small thing which does not concern you."

-TFoH Ch. 53, p. 900 (paperback)

This is why she had a "small bubble of hope" when she attacked Lanfear. She had seen in Rhuidean that she had to pass through the ter'angreal with Lanfear, but she had some hope that she would somehow survive based on Min's vision that she would marry Thom.

Since there is no evidence that the "woman dead and gone" viweing has anything to do with Moiraine, it is very plausible that it is Lanfear that Rand needs. This is possibly corroborated by something Lanfear said to Rand:

"Remember that I am your only hope of surviving, my love." -TFoH Ch. 6, p. 177 (paperback)

While this may be Lanfear BS'ing Rand, it is also possible that it is true.

How does Rand get Lanfear to help?

A few books ago, this wouldn't have been a problem. She wanted to overthrow the DO with Rand. But now she hates him, and is mindtrapped, so how can she help? This is where my theory that Rand and Moridin will merge comes in. Min had a vision in ACoS:

"I saw you and another man. I couldn't make out either face, but I knew one was you. You touched and seemed to merge into one another, and...one of you dies, and one doesn't."

-ACoS Ch. 33, p. 526 (paperback)

Rand thinks that this refers to him and LTT so that must be wrong. Lately, we have noticed a third person within Rand, called "the other" or "the third destroyer". I think this "other" is none other than Moridin. He and Rand will merge and one will survive and the other will die.

The Other is a result of Rand and Moridin crossing BF streams

The other and Rand's OP sickness are both the result of Rand and Moridin crossing BF streams in ACoS.

"Just thinking of that, of the two streams touching, made his vision double again. Just for an instant, he could see the man's face again, sharp where everything else had blurred.

-ACoS Ch. 41, p. 848 (paperback)

This is the first time that Rand's vision doubles and also the first time he sees the other face. The next time we see Rand is the first time his OP sickness is ever mentioned:

For an instant, he saw double; the world seemed to tilt dizzily. That was a recent problem, and he worried it might be part of the sickness that killed men who channeled

-PoD Ch. 13, p. 325 (paperback)

And a few chapters later, we have the first ever mention of "the other":

when he saw himself in a dream, it was not always himself at all that he saw. It was not always Lews Therin, either, the face he had come to recognize as Lews Therin's. Sometimes it was blurred, yet vaguely famaliar, and Lews Therin seemed startled by it, too.

...

The dizziness faded quickly, the twinned sight a little more slowly, as it always did these last few weeks

-PoD Ch. 21, p. 460, 464 (paperback)

We can see the sickness gradually getting worse throughout PoD and WH as Rand sees "the other" more often.

For an instant, he thought he saw a face. Not with his eyes; in his head. A man, shimmering and unrecognizable, gone.

-PoD Ch. 29, p. 644 (paperback)

I thought I could build, Lews Therin mumured in his head. I was wrong. We are not builders, not you, or I, or the other one. We are destroyers. Destroyers.

-WH Pro, p. 80

The only new thing from CoT is Rand's monologue in his head about the Creator. He says that it didn't come from him, so it must have been LTT...except that LTT had been nodding along as if listening to someone else and agreeing. This monologue seems very similar to the musings of a certain Elan Morin Tedronai.

Rand will end up controlling Cyndane's mindtrap

If Rand and Moridin do merge, Randin will have control of Cyndane's mindtrap. If this is Rand, then he can make her tell him how to defeat the DO and help him use the CK to seal the Bore.