Add space, a moving Moon, and a physical Sun that burns you.

Remove the current playable world border and instead create a world limit like the one from the first Minecraft test version, but millions of times larger while still being limited. It should be like our planet: limited, but still absolutely gigantic. Also add a survivable void. When the player reaches the void, they should eventually be turned upside down and returned to the bedrock, so they always end up standing on the bedrock. The void should be completely dark. And if the player flies far enough into the void, everything should eventually become completely black, with stars visible in the distance.