The boats are going to have a real handling model and that is the thing I am most sure about

Watch how the hull sits when they come off plane. The bow drops, the wake collapses forward, and the boat squats before it settles. That is not a canned animation, that is buoyancy responding to throttle.

Every GTA boat before this has felt like a car with a water texture under it. If they have actually modeled displacement and planing, the Keys become a completely different place to play.