New Survival after defeating the Ender Dragon

Kind of like having a second quest. You would teleport back to your over world, but with some changes to mobs to increase the difficulty of survival, and changed structures and new items to craft, or new treasures to find.

Mobs and Treasure Chests loot tables change with unique items you can only get after you return.

Stronger mobs, either indicated by different behavior and/or appearance and more difficult to kill. Perhaps the behavior in spawning changes as well and more aggressive.

Structures that you find, like Temples are harder to raid. Perhaps the traps are different and/or when you reach a spot in the Temple, mobs will automatically spawn.

Giving a use and function to the Ender Dragon Egg. Collecting it and bringing it back to the overworld grants the player some of these additional benefits and buffs. Like adding a new GUI to the Beacon with an Ender Dragon Egg slot and works within a radius which could effect the Enchanting Table.

Having access to more powerful enchants, the 'Too Expensive' cap could be higher and the cost to enchant could be higher as well,

Raids in Villages are harder and Pillagers would attack the players home base and destroy stuff like the Beacon.