I'm starting to think they may have taken Barbossa in a Governor Henry Morgan direction, and officially have him be a retired pirate in this film running an island in exchange for services to the crown. Salazar sparing him and trying to use him to find Jack wouldn't make that much sense if Barbossa's just the pirate captain of a magic ship that still can't catch the Pearl, nor would it make much sense if that's the same case and he's just a privateer. However, a Governor Hector Barbossa? With control over an islands resources and a small flotilla including the Queen Anne's Revenge? I can see that being useful to Salazar, and perhaps even the honor of the position would encourage Salazar to treat Barbossa like a fellow gentleman.
And who knows? Perhaps Barbossa will have a subplot of trying to wrangle Henry, Caterina, and Jack into stopping Salazar all while still pretending to follow Salazar's orders.
Also, the trailer seems to be playing Henry as having a funny combination of Will and Elizabeth's personalities when they were law abiding, with some of Elizabeth's endearing idealism and Will's properness. Just the dorky smile he has when he says "I saw her ankles!" Seems to speak of his parents, and for some reason I love the idea of him being this dork with Jack as an honorary dirty uncle.