Here's my long list of things I'd like added.
More weapons like crossbows, spears, shields, and maybe flintlock guns.
Adding hydration that kills you if its gone (like hunger) and heals you when its full. Drinkable items to hydrate including water, apple juice, milk
Food and drinks all have different hydration values.
Freezing to death
A gold metal, that combines gold and iron to make a stronger substance, and tool tier for it
Expanding on the Nether and End, mostly the End. Just adding Nether Quartz made the Nether much more interesting, so maybe an Ender Crystal Ore?
A Copper tier of tools in between Stone and Iron. Copper would be alot more common than Iron, and Iron would be less common than it already it.
A gamerule that toggles the ability to break blocks. (ex. /gamerule breakBlock false)
A fly command
An RPG gamemode that generates world with new generated structures, like Native Villages, Ninja Dojos, Pirate Ships, and Castles.
Cloth armor (that looks like a cloak and is dyeable)
Wood Helmets and Chestplates (Increase chance to die from fire)
Fish (so fishing is more fun) and Sharks (that are hostile)
Deserted Island Biomes, with buried treasure, coconuts, bananas, and Monkeys (you can tame)
Tomatos and Cheese, so you can make Pizza
Batwing drops from bats, would be used to make blindness and naseua potions
Magic items, including Magic Wands and Elemental Enchantments
Tinted glass
Another dimension (not neccessarily the Aether)
More boss mobs, including Herobrine
What do you think?