I had the thought that in the next book or two Rand will convince Moridin that he was wrong all along and he shouldn't despair of the Light ever truly win against the Dark One.

Their talk in the dream world made them seem almost like friends. Rand is trying to convince him there that there is room for hope but Moridin is despondent. So maybe new hopeful laughing Rand will succeed in presenting his arguments better the next time they meet and Moridin will change his allegiance before the end.