Maybe Verin's letter will also reveal clues about the identity of Slayer as Isam and Luc. After all, Verin was in the Two Rivers at the time when Slayer was there, and remarked that the Trollocs screaming "Isam" is "interesting" (she also knows the Dark Prophecies). If Moiraine is rescued, it makes sense that Mat will bring her to Caemlyn first, where also Slayer's arch enemy Perrin might be. There Moiraine, Perrin, maybe Noal (if he raised Isam) and Co. might put things together about Slayer. Though if or how that will be important remains to be seen. Maybe Slayer will also be important in the endgame against the DO..