World's:
-Strongest Man
-Strongest Creature
-Strongest Swordsman
I don't expect Oda to make a Strongest Woman, since Man is taken to mean "Human", nor do I think there will be titles associated with other combat styles/weapons.
However. IMO we're in for a World Strongest Will for the best hakiman, either Shanks or, revealed later on, Roger himself. A title which Luffy might get after Rafter.
Also. Considering Kaido's title in retrospect, I wonder if we'll get some other flashback sob story about Oni and Oni-descendants being viewed as inferior to humans (hence Strongest Animal).