I have been very interested in command blocks, and have been messing with them for a long time. One problem that I found with command blocks is that you could not have a player easily edit commands for awesome features. You could not get the skull of a random player that is playing without plugins/mods. You could not do a lot of stuff. Here are some ideas that I think would be interesting to add.
Scoreboard "string" objective
This scoreboard is similar to the dummy objective, except it stores values as STRINGS