I read an interview in which Brandon said that one of the POV characters would be an engineer-type researcher, so I am quite sure Navani will be a POV character and probably get a book - she could also give great insight into Gavilar's actions from another viewpoint. Since Gavilar's secrets are sort of at the center of the mystery, it would be very interesting story-wise to get her viewpoint, too. Plus, needs more women than just Jasnah and Shallan.
On the other hand, I don't think Elhokar will get a book, or even viewpoints. He is just too one-dimensional of a character for me - definitely not the most elaborate character in the book by far. That indicates to me that he will be more plot-device than viewpoint character in the future - I vote him most likely to turn to the dark side, whatever that might mean on Roshar. Also, Jasnah can give all the input on Gavilar from a perspective of his child, and we know she will be a viewpoint, so Elhokar's history is not likely to be all that interesting.