It would be really awesome if I could play this game from the couch with built in controller support. There are controller mods but they don't include the launcher or world selection so I would still have to get out my mouse and keyboard, and the mods aren't as good as real controller support. Adding controller support isn't terribly difficult so the only part that would take a little work is changing the UI. Settings for button remapping, sensitivity, and deadzones would be very important.
A sort of sub-suggestion for this would be actual split-screen on PC but that would be a lot to ask.
EDIT: With Valve's Steam Machine and SteamOS projects living room PC gaming is likely to become more common, so adding good controller support seems like a smart business move for Mojang.
I used the search button, my suggestion is different as it includes the launcher and world selection as well as native splitscreen instead of having to use LAN and multiple windows. Controller support is a pretty basic feature that a lot of games have now days and it isn't hard to program.