Ellison has been trying to build toward making sailing a TV sport. So, faster boats, that complete the races in half the time, in spectator-accessible venues, near shore. He wants to use these same boats each time, so that you're not building from scratch every single time, and you don't have weird races where one team shows up with an invincible boat.
But, by the rules of the trophy, New Zealand can make the next boats whatever they want.
Usually the defender and the challengers negotiate, so that one doesn't show up with a trimaran and one with a traditional yacht, but if they don't, things just revert back to the Deed of Gift: Boats no more than 90 feet long or 90 feet wide, racing on salt water. Those are the only guidelines. Which is kind of how we got here.