Redstone Update

The Redstone Update is a planned major update labeled as 1.5. It was announced at MineCon 2012 at the Future Updates with the Minecraft PC Team and The Future of Mod API talks. It may be released sometime in January (or possibly February) 2013.

Planned changes
Note: Most of the changes listed here have no detailed references since most of them were mentioned at MineCon, especially the Future Updates with the Minecraft PC Team and the The Future of Mod API talks.

You can watch the presentation here:

General
The features were:
 * Rewriting rendering engine
 * Will require a higher OpenGL feature-set
 * Will include some sort of fallback for older hardware
 * Much faster overall rendering, resulting in more frames per second (FPS).
 * Lighting fixes similar to the ones first introduced in snapshots 12w39a/b (during 1.4 development)
 * Support for fancy lighting control
 * Support for more realistic lighting, such as active furnaces only giving off light from their front surface
 * Improved Texture Packs
 * Textures now use one file per block/item, which are stitched together at runtime, texture sizes don't need to be consistent
 * Any block and item can be animated by putting the frames underneath each other in the right .png - Use an optional .txt to specify frame order and duration
 * Special rules apply for water, lava, compass and clock
 * Existing texture packs will "automagically" be converted
 * Vanilla textures will be used if texture files are missing
 * Support for high resolution textures
 * Not intended to support HD skins
 * See the wiki's page on texture packs for more information

Gameplay

 * Redstone Improvements
 * Containers like chests and dispensers give off a redstone current that equates to how full they are
 * More predictable and consistent redstone behavior
 * The functionality of BUDs may be affected
 * Eliminating directional quirks
 * Most of the timings of redstone contraptions will change
 * Overall redstone will be more like analog signals
 * Redstone signal strength will matter (for some blocks)
 * Better Inventory management
 * Double-click items to fill the stack up as much as possible
 * Drag item stacks around to divide them up over the dragged-over slots
 * Drag item stacks around with the right mouse button to place one of that stack in each dragged-over slot, if that slot is not occupied already
 * Shift double click items in a crafting area to place all items in the inventory
 * Shift double click an item stack to move all other item stacks of that kind to that part of the inventory
 * Pressing Q while the mouse is over an item in the inventory or a container to drop it
 * Added & Improved Death Messages
 * Now include the cause of death, the player the deceased player was fighting at time of death, and the name of the item used to kill
 * Player fell off a ladder
 * Player fell off some vines
 * Player fell out of the water
 * Player fell from a high place
 * Player fell into a patch of fire
 * Player fell into a patch of cacti
 * Player got finished off by Player/Mob using Weapon
 * Player walked into a fire whilst fighting Player/Mob
 * Player was burnt to a crisp whilst fighting Player/Mob
 * Player tried to swim in lava while trying to escape Player/Mob
 * Player walked into a cactus while trying to escape Player/Mob
 * Player was slain by Player/Mob using Weapon
 * Player was killed trying to hurt Player/Mob
 * Improved renaming (using the anvil) of containers and mob eggs
 * Mobs spawned from renamed eggs have the name of the egg and the names will appear in the death message
 * Mobs can now display their custom name as nametag using an NBT tag
 * Renamed Chests, Trapped Chests, Dispensers, Furnaces, Brewing Stands, and Enchantment Tables will display the new name in their GUI where the normal name used to appear
 * Updated language files
 * Language files can now be updated via the background downloader (no need for a new Minecraft release)
 * Improved Options
 * Moved Texture Packs button to options menu, instead of title screen
 * New Chat Settings in Multiplayer Settings
 * Scale, Focused Height, Unfocused Height and Width is now configurable
 * Added new Command
 * command for analog signal output, can be used in a Redstone Comparator placing a Command Block in 1 block near
 * Fixed many bugs
 * Fixed dropped anvil making no sound when it breaks
 * Fixed linux users being unable to open to LAN because it's bound to 127.0.0.1
 * Fixed piston arms sometimes becoming invisible when pulsing quickly
 * Fixed powering a redstone wire with a stronger signal not always propagating the newer signal fully
 * Fixed dispensers shooting whenever they are updated while powered
 * Fixed pulse length and delay being inconsistent with certain torch and repeater combinations
 * TNT explosion being delayed until exiting and re-entering world
 * Minecart noise gets stuck on long cart rides, (bumping, choppy sound) fixed
 * Fixed Minecraft VERY slow to join/update a server, takes LONG time to login (30 seconds/ 1 min)
 * Tile entity crashing bug fixed
 * Fix for random black spots
 * Fix for some rendering bugs

Blocks & Items

 * Redstone Comparator
 * It is the same as a repeater, but with 2 inputs
 * If input A is stronger or equal to input B, it either repeats the signal or outputs a fresh signal
 * Output is toggleable by right clicking.
 * If input A is weaker than input B, then there is no output.
 * All containers output a redstone signal when a Redstone Comparator is placed against it directly. The strength of it depends on how full the container is
 * Large/double chests can now release a redstone signal when connected to a Comparator depending on the amount of stacks within. Before, double chests would only emit a signal depending on how full each individual chest was (a double chest with only the the top half full would emit a full signal from the side that the items were in).
 * This works with Trapped Chests as well, meaning it can provide two redstone signals with different causes at the same time
 * Hopper
 * Places and takes out items in Hoppers, Chests, Furnaces, Minecart with Chests, Dispensers, and Brewing Stands.
 * Allows for the automation of many processes collecting the drops
 * Powering the hopper now also stops it from taking in items
 * The redstone signal emitted when a Comparator is placed against it directly
 * 1 item will give a signal strength of 1, a 1/3 of a stack (21 for items which stack to 64) gives a signal strength of 2
 * The number of full stacks x 3 = Signal strength
 * E.g. 2 stacks of an item/block will give a signal strength of 6, while 2 potions will also give a signal strength of 6 because a potion occupies one stack). 1/3 of a stack
 * Dropper
 * Works much like a dispenser, but it doesn't use items; it only drops them.
 * Also works like a Hopper, but it needs redstone to make it travel and it needs a storage block directly in front of it.
 * Trapped Chest
 * Gives out a signal depending on the amount of players looking inside. 1 person = 1 strength signal, 2 people = 2, etc.
 * Crafted with a Chest and a Tripwire Hook.
 * Large Trapped Chests can be staggered with Large Chests to allow more compact storage.
 * Transmit signal downward through one block. This does not apply horizontally (through walls)
 * Texture is slightly different than a normal chest, with a red stain around the latch.
 * Weighted Pressure Plate
 * Used to detect item entities
 * Gold version reaches full strength at 60 items.
 * Iron version reaches full strength at 600 items.
 * Linear, so 10 strength signal means twice as many items as a 5 strength signal.
 * Block of Redstone
 * Stores redstone dust similar to blocks of diamond, etc.
 * Emits constant redstone power
 * Works as pushable redstone power source
 * Nether Quartz
 * Is a crafting ingredient for Daylight Sensors and Redstone Comparators.
 * Can be crafted into decorative blocks.
 * Daylight Sensor
 * Outputs a signal with a strength corresponding to the intensity of the sun
 * Nether Brick (item)
 * Obtained by smelting Netherrack
 * Crafting recipe is 2x2 Nether Bricks.
 * Nether Quartz Ore
 * Drops 1 Nether Quartz item when mined, and is also affected by the fortune enchantment.
 * Block of Quartz
 * Stores Nether Quartz similar to block of diamond, etc.
 * Quartz Slab
 * Quartz Stairs
 * Chiseled Quartz Block
 * Pillar Quartz Block
 * Pillar Quartz Blocks can be placed sideways.
 * Improved Lava
 * Texture changed
 * Improved Water
 * Creating a infinite water source no longer needs a block underneath, but has to have a water source block.
 * This means you won't ruin rivers/oceans with Buckets
 * Activator Rail
 * Used to trigger Minecart with TNT
 * Needs to be powered by redstone
 * Transmits power up to 8 activator rails far
 * The crafting recipe includes 2 sticks, 1 redstone torch and 6 iron ingots.
 * Minecart with TNT
 * Triggered by Activator Rails
 * Crafting recipe is a TNT block on top of a minecart (allowing for creation in the 2x2 inventory)
 * When it derails, it explodes instantly, ignoring the usual timer delay
 * Explodes even more violently the faster it goes
 * In Creative mode when left clicked while moving, the Minecart with TNT explodes
 * Minecart with Spawner 
 * Minecart with Dispenser 
 * Minecart with Hopper 
 * Pass items to hoppers while passing on a rail with a hopper underneath.
 * Don't need a activator rail to use
 * The possibility of linking minecarts together (driven by furnace minecarts)
 * Rail to unload mobs and perhaps players when reached
 * Changed Locked Chest texture
 * ''' Removed unused Smooth Stone Slab
 * Jeb announced on reddit the 'Smooth Stone Slab' will not be removed and it's data value will become 43:8 (and will remain so) with the "possibility it gets officially added in the future" as stated by Jeb in the comments. 

Mobs

 * Improved Skeletons
 * Now shoot from 15 blocks away, instead of 10
 * Skeletons shoot players one block away, depending of difficulty
 * Skeletons shoot faster when you're closer to them, depending of difficulty
 * Improved Zombies
 * Burning zombies now set the player on fire (increased chances of ignition with increased difficulty)
 * Improved group attack

World Generation

 * Nether
 * Added Nether Quartz Ore around the Nether to encourage exploration of the dimension
 * Abandoned Mineshaft
 * Now spawn items on Minecart with Chests, instead of Chests