Horse Carriages
More animals (Bears, Lions, Better Rabbit Design because...wow, Wolves, Birds etc)
Diseases like Colds, the flu, maybe even a plague? etc...
More of a purpose to Villagers...
Something better than Diamond
MODDING API HELLO
Sailboats/Ships/Pirates/Something more in the Ocean
Maybe more. Don't know.
But not anything like guns, cars, bombs or anything like that. Like someone else said i believe, It just doesn't fit it with minecraft's theme.