Hank definitely needs a backstory now, it wouldn't surprise me if we ended up with some sort of a sidequel about him.
Hank has become one of my favorite Pixar characters after seeing the film. There's so many unanswered questions that feel like they could have been, but they wanted to keep the pacing peppy enough for film runtime. Something that's a habit with Pixar films. I'd love to see more Hank of some kind, and if there's a way to make so much as a short about why he hates the ocean, something that's kinda a polt hole at the end of the film, I'd say it needs be done. I'm sure the Blu Ray has some deleted scene about it, but there's enough material there for something.