To me the image looks like a cryptic with a strange head. Maybe Ishar succeeded in bringing a spren to the Phisical Realm after it had became a host for Yelig-nar? It's hard to tell because we can only see the shadow on the right one though.
i
I think that the theory is pretty solid other than Jasnah. i think that we're going to learn about a disease that Jasnah had as a child.
maybe it ties in with why she hates bandits so much?