Will there be rewards for being ranked high in the future (other than being able to do /rank and show a glowing animal head over your character)?

Qualifying for global tournaments is one reward, and a very large one. Fame is another marker of your success, so the "glowing animal head" is actually a pretty cool thing. After all, if you're looking for a pick-up group, there's nothing like a Badge of Badger or Crown of Critter to reveal you as the best choice for a group. :)

But yes, rewards will be expanded in the future. In fact, there are some major changes being worked on as far as rewards for PvP, but mum's the word on those for now.