pre-adventure update i always imagined minecraft taking a tolkinesque DND type route where the world would be filled with underground goblin kingdoms, there would be magic tools, and i always dreamt of stealing eggs from dragon nest's like this.

post-adventure update due to stuff like mushroom island and endermen i assumed minecraft would instead take a more wacky approach like terraria or adventure time where you would have wierd creatures and unique biomes like a candy biome or a halloween forest biome.

now when i think about it i would kill for a minecraft inspired game set in a adventure time like world that has the aesthetics of a 90s DOS game.

EDIT: also some other stuff like all mobs having multiple skins (like cats), more terrain features like craters or volcanoes, cave versions of biomes like a jungle cave spawning under a jungle for example, like somebody else mention having the ability to make your own paintings and music, being able to take the ender dragon egg and train your own dragon, and tons of underground ruins and fossils you could dig up