Sharks do seem cool, but Mojang has already stated in the "Previously Considered Feedback" page that sharks will not be added. TheRPGAdventurer has part of the reason, that being sharks dying in real life is a genuine problem and should not be encouraged in video games aged for children, but the specific reason given is that hostile mobs are meant to be fantasy creatures, not real ones.
"No realistic sharks. Hostile mobs need to be fantasy creatures. (2018, but since folks ask so much it's at the top)"
But as long as the idea is reshaped into a fantasy shark and not one that mimics real life, it could still have a shot.