Tim Zahn wants to write more Thrawn books in the new canon:
https://www.starwarsnewsnet.com/2017/04/timothy-zahn-wants-to-make-more-thrawn-books.html
The idea they mention for a story about Thrawn’s relationship with Vader doesn’t really float my boat, but I’m hoping he’s got some more interesting ideas that he can’t go into so as not to spoil anything on Rebels. I’ve said this in the Rebels thread already, but I’d love to see Thrawn disappear into the Unknown Regions at some point next season and then reappear later in the timeline. Zahn claims he wants to write four Thrawn books; I can’t imagine they’d all be set between III and IV.