A 3 way battle between the 'good guys', Shadowspawn and the Seanchan could be a good way to bring the Seanchan to the Light. The Seanchan either launching a major attack on Caemlyn (as they see Andor as a way to encircle Rand to the South and take out a powerful kingdom) and then being attacked by Trollocs in turn. Or Caemlyn is attacked and the Seanchan Travel there only to find the city on the edge of defeat. They are faced with the choice of retreat or commit their forces.

It won't happen, but I'd like to see the last third of TOM as:
1. Shadowspawn attack Caemlyn
2. They are on the brink of defeat when the Seanchan arrive
3. The Seanchan engage the Shadowspawn, taking heavy casualties
4. They have enough forces though at the end to take Caemlyn
5. This is when Mat appears with Rand, with enough forces to take the Seanchan. Mat's dragons toast a few thousand Seanchan making them realise they are stuffed trying to engage Rand's/Mat's forces from then, even with Travelling. They either ally or retreat awaiting attack.
6.Rand binds the Nine Moons to him (much as I'd love to see this involve Rand slapping an a'dam on the Empresses neck and parading her wretching and screaming in front of the Seanchan nobles, I'll take it being via Mat's marriage to her) and they all prepare to head north.
7. End of TOM.