Redigit (Terraria creator and lead programmer) posted some spoilers on their IRC last week regarding the upcoming 1.2 patch and what you can expect in the future. [Source]
• Player and World limit increased to 1000.
• Chests are double-sized.
• Hallowed armor is around 4th best.
• Inventory now has one more line.
• Character screen has HSL interface (Hue/Saturation/Light) Shown here.
• 999 item stacks.
• Terra blade is the most powerful sword, but not most powerful item, others are better.
• Orichalcum armor with good set stats, numbers and effects.
• He's considering another slot but there are more tinkers now.
• Ton of new backgrounds set during world gen, drawn by Crowno along with a new Phoenix Blaster sprite.
• Crowno was hired after his "best t-shirt design" in the contest, Red appreciates his work tons! Credits to Crowno!
• "Ice biome is kind of an alternate version of the regular underground, slightly harder w/ better drops to break up monotiny."
• Large map with all revealed.
• Jungle dungeons are hard to get to, entrance has to be earned but no dungeon guardians of sorts.
• Jungle Shrines are still there.
• There are yet more biomes than have been shown, tons of items and NPCs unrevealed.
• If you inflate the item count a tad, 600-700 new items ingame now (Again, exaggeration).
• Dyes and paint are about 100 of those items.
• There are 12 base colors for dyes, and then different versions of those and gradients, etc.
• You can make Gold look like Titan.
• Still gonna do some more item/armor tiers, boss drops, rare drops, super rare drops.
• Redigit has been reading TerrariaOnline to see all the suggestions and what people want, some that have inspired him.
• He's making lot of effort to make playthroughs unique, aka things that are in one world aren't in the other.
• "Ebony is more or less Ebonwood" (This does not spread corruption).
• There is a very valuable set of things that happen in hardmode to help you fight the spread (More than people know of) and you will gain a lot more control of how your world is.
• Possibly a new time changer, and less likely chance of biome converting procedure. He's playing around with the idea of controlling time/events, but no promises.
• He also considers implementing gear/accessories that help with building.
• He's considering taking stuff from the console version, like the autodig (Hold down a hotkey, like CTRL, to remove all blocks/walls in that direction, Hold down CTRL to remove all the tiles in the direction of the mouse to make a tunnel the size of your character).
• He thinks Mounts could be super fun.
• Terraria 2 will be 2.5D.
• Terraria 3 will be 3D.