I recently made a post for a mod Idea Here
Concise version: I want food to be useful... sort of force the player to eat a variety of food and require more food throughout the day, with buffs and debuffs and a new Starvation meter.
Or, if you don't feel like that one... Another is the Dungeon Dimensions, a mod where you can find golden doors around y level 6-7 in an obsidian room, when you go through the doors you are taken to a dimension that is its own dungeon, a long and complex dungeon with new mobs and even bosses with their own strategies to defeat them. You cannot break or place blocks in the Dungeon Dimensions (basically you are set to Adventure Mode) and you can find rare and powerful equipment hidden in these dungeons along with legendary equipment from the chest after the boss. Some rooms would require you to clear all mobs in the room, optional rooms with puzzles, and even platforming rooms, each optional room leading to a chest with loot in it. The dungeons would be randomly generated each time and the golden door would always lead to the same dungeon. The door can be broken but would drop a gold block.
Hehe... A third idea would be GraveStones, left behind when and where you die, they would store all the items you had on you when you died and would drop them when broken.
Sorry for so many ideas... I just don't have time to learn enough coding to do these... Really wish I did, I used to mod but my job eats all my time and Minecraft eats any that is left.