Being a colossal smash and money printing machine, there's not much more that can be done to Minecraft to make it more successful. So it's good to hear it's developers aren't really trying.
Instead of continually adding new stuff to the game from their end, Mojang has decided that the future of the game lies in the thing that's made it so successful to date: its user-generated content.
To that end, the team tells PC Gamer that they're hard at work re-writing the bones of the game from almost the ground up, so that in the near future they can release an official editing suite for the game (currently creating and installing mods can be a little too tricky for the casual user). Mojang is also looking at hosting their own private servers, so small groups of everyday users can build their own persistent worlds and experiment.
If the game as it stands can already support working computers and games of Team Fortress 2, it'll be interesting to see what the masses can come up with once modding is made easier.