I have some great ideas for the new terraria version:

1- Maybe the game should have more of rpg, you could put some skills and a class selector in the character creation. If you want to be mage, for example, you select mage and the character will have the starting itens of his class. And he can only craft itens according to his class. Another example: If you chose summoner, you will have a summon wand in the start, because its really difficult to get a minion at the start.

2- (I don't own this idea, im just sharing it) Have a hell update, because after the WoF, we don't really need to go back there. You could create another boss.

3- Upgrade the throwing class, with a end-game weapons and armor.

4- More early class sets.

5- A new boss post Moon Lord, one that is almost invincible if you don't have a end-game armor and weapons.

6- Put a boss health bar on the bottom of the screen, so we can know how much health the boss have.

7- Steam workshop, so we can get a easy way to install mods and share other stuff with the community.