Once you get maxed out netherite and unlimited totems the only way to die is the void. The deep dark and the ancient cities is an example of what is needed to make it more fun and challenging. Also you dont need to go mining for diamonds because you can get it from villagers in minutes.
Adventure 2.0. Currently in minecraft once you reach the part where you are completely overpowered, the adventuring part become way too easy. It could add more structure, mobs and maybe nurfing the current features.