I have an idea. Maybe add in floating lake islands, which could have their own special mobs for them. For example, there could be an aether crocodile, that leaps out of the water and tries to grab you. There coukd maybe be a dungeon for that island type. Also, maybe make a function for Aerwhales, such as making a way for them to be ridden or something.
They should add cockatrice nests, make passive mobs more common( its a miracle to find a sheepuff right now) and let you put armour on moas (maybe put orange moa back in). Also, maybe make swets tameable again? Dragons might also be a good idea, but they should be tameable ( like hatch the dragon egg in an incubator to get a tamed ender dragon)