First, Mojang introduced hunger. That was good, as it added realism to Minecraft. Then they made it so that you had to draw back your bow before firing. That was also very realistic. I have some other ideas that Mojang may like that will make Minecraft almost as real as life itself.

A. Gravity Affecting Blocks More
1. Floating islands will fall to the ground in this new "Realism Update".
2. Caves and mines not properly supported will cave in.

B. Heat and Cold
1. When near fire or lava, convection will eventually burn the player to death.
2. When in cold and snowy biomes, the player will eventually freeze to death if not wearing wool armor.
3. When in deserts, the player will eventually get heatstroke and die.

C. Interdimensional Travel
1. The Nether and The End will no longer be accessible, as these are not real.

D. Food
1. Food will spoil 3 days after it enters play.

E. Disease
1. A wolf will have a 1/200 chance of infecting the player with rabies when angered.
2. Eating raw beef will have a 1/145 chance of infecting the player with mad cow disease.
3. Diving underwater in a swamp will have a 1/1000 chance per second to infect the player with flesh eating bacteria.

F. More Accurate Damage
1. Falling too far will break the player's legs, slowing him/her to a literal crawl.

G. "You Only Live Once"
1. Respawning will be permanently disabled, and the only difficulty will be Hardcore.

H. Only Real Mobs
1. Creepers, Skeletons, Zombies and the like will completely disappear from Minecraft. There are no creepers IRL, nor are there zombies or animated skeletons.
2. Spiders will become very small and easy to kill.

I. Exhaustion
1. Aside from the hunger system, there will be a new Stamina Bar.
a. This will deplete slowly as the player mines, walks and does other things.
b. It will be replenished by sleeping in a bed.
c. If it depletes fully, the player will start taking damage.

J. Thirst
1. The player will take damage if this meter falls to zero.
2. The player must drink water to replenish this. The water must be collected in a bucket and boiled in a furnace before drinking. If the water is not boiled first, the player may contract a disease.

K. Electrical Wiring
1. Redstone will be removed from Minecraft, as this element does not exist in reality.
2. Copper wires will replace redstone.
a. Wires must not cross, or they may start a fire.
b. Wires will eventually corrode, requiring replacement.

L. Potions
1. Potions will no longer be an element of Minecraft. This will be replaced with Herbalism.

M. Herbalism
1. The player must find and cultivate wild herbs for medicine.
2. Herbs will be used to treat some diseases.
3. The player may become addicted to certain herbs.

N. Enchanting
1. This will not be available any more. Such activity is seen as witchcraft in reality and should be avoided.

O. Experience
1. The player has certain skills, such as mining, crafting, fishing, woodcutting (Runescape much?), etc.
2. Experience in a skill will determine how much the player can do without becoming exhausted, and how efficiently the player can do the activity.
3. There will be no gauges that show the skill levels, because one cannot tell one's experience in levels IRL.

These all seem very realistic, and if you liked hunger and the new bow, you'd probably like these.