I love MC but I think a-lot more can be put into the game. My ideas are;
1. More weapons- Battle axes are slower than swords but do more damage. Hammers stun enemies. Crossbows take a long time to charge but kill in one shot. Shields completely deflect attacks. Spears have longer range. Wizard's staffs can be enchanted to harness elements and use different attacks.
2. NPCs- NPC towns and cities are bigger and better than villages but are more rare. NPC soldiers can be hired via emeralds to defend or follow you. Also you can equip them with weapons.
Miners, loggers and builders can all be hired or if just left alone will mine, log, or build.
NPC kings are in castles and if given jewels will give you an army.
Boars are hostile versions of pigs.
Bulls are be hostile versions of cows, but are passive when given wheat to mate. (will stay passive)
Giant insects are in jungle and desert biomes, some are hostile, some aren't.
Fish and whales are in ocean biome.
Frogs are in swamp biomes.
Deer are killed for skin which can make clothes. (no armor but cool)
4. Biomes and structures-
Coral biomes are full of life and contain sea plants that can be eaten or used as building blocks.(coral)
Alpine biomes are snowy mountains.
Castles are full of NPCs and have an NPC king.
You gotta a lot of cool ideas, some of which could contribute to good adventure maps or really good gameplay. But a lot of it, specifically the weapons and larger NPC towns would take more effort to code and I'd rather (personally) have some tried and true Minecraft updates before we get our own unique stuff like that.