Before i list what I am looking forward to I would like to see something. I believe 1.4 is the last BIG update for Minecraft. What else could you possibly add? This is it. After this Minecraft can be called finished. Jeb needs to move on to a new game.
I am looking forward to New Mobs, mod API, wall clocks, connected maps, colored leather and invisibility. While I am not looking forward to cobble walls I think they will be cool. Flower pots should not be added and beacons are expensive self enchanting pyramids. I hope this mod API truly will make modding and plugin making/updating easier.