I haven't thought this all the way through yet, but it occurs to me that we all assume Tuon will be the one whose actions bind the Nine Moons to serve Rand. With Mat now Seanchan emperor though, couldn't it be just as likely that Mat might use his newfound Seanchan authority to commit to a truce/alliance with Rand, with or without Tuon's approval? I can't remember reading anything about the authority of an emperor in relation to the authority of an empress, but any such info could have a bearing on the plausibility of this idea.