I posted this in the Mat thread a couple hours too early; it definitely belongs here. The issue of the damane is obviously significant, and it is an issue that I expect to see resolved before the Seanchan join with Rand's forces for the Last Battle. We know that the Seanchan originally collared the Aes Sedai to prevent them from using the One Power to gain dominion over non-channelers and to give Luthair's army a significant boost in firepower. The damane are still viewed as too dangerous and useful to allow them autonomy. I think that the combination of Mat's foxhead medallion and his cannons will allow the Seanchan to free the damane.
In the other three societies in which we have significant insight into the lives of channelers, we know that the women are restrained by social structure (the Oaths, the cultural prohibition against Wise Ones participating in battle, the strictly defined command structure of the Athan Miere). It is unlikely that such a structure would spontaneously arise were the Seanchan to suddenly free the damane, so they need something else to insure that they don't revert back to the continent's original state (warring Aes Sedai vying for power). The foxhead medallion provides a unique solution to this problem. I see this playing out in one of two ways:
a) The Seanchan require all channelers in Seanchan territory to wear a copy of Elayne's flawed medallion, preventing them from channeling.
b) The Seanchan make copies of Mat's original medallion available to all Seanchan citizens, granting them immunity to weaves.
I find b) to be significantly more likely, primarily because a) seems to be unenforceable. The two disadvantages to b) are that you have to produce millions of Ter'angreal and channelers can still drop a rock on your head. Fortunately, the Seanchan already have a booming Ter'angreal industry from producing a'dam. The second problem will be addressed later.
The Seanchan armies rely on the firepower than damane provide, and that is not an advantage that they will easily give up. In a stroke of luck, Mat has just discovered gunpowder, an invention that will make the damane obsolete. Cannon are capable of being every bit as devastating as damane (particularly given that damane cannot form a circle), and they can be made in much greater numbers. From Aviendha's visions, we know that personal firearms are right around the corner (these will negate the rock on your head issue from above). The Seanchan way of waging war is about to become extinct. The proliferation of gunpowder will make the damane unnecessary from a military perspective.
In conclusion, I believe that Rand will be able to trade the knowledge of Mat's medallion and cannon in exchange for a promise from Tuon to begin the process of freeing the damane (presumably Wise Ones, Aes Sedai, and Windfinders immediately, with the native Seanchan slowly integrated back into society after the Last Battle).