Adding a game explorer tab next to every game!
Combining the actual game, the analysis board, and conditional moves into one very clever and inovative combined board.
I would like a note that pops up every time i click the submit move button that says: "Have you checked to make sure that this move is not a blunder?" :-P
Agree with the vote chess list that was already suggested.
Add a new time control for onlie chess, 10moves/day or "20moves/2days" in which each player must make that number of moves in that time or loses. I like to play faster games on online chess, so that they take only a couple days, and this time control would help me find others that would do the same.
Adding features/functionality to Mobile Chess. The following are listed in descending order of 'wishes': (1) Allow user to review games in progress; not just games that are pending; (2) Play against a chess engine with varying levels of difficulty; and (3) access to daily puzzle, tactics trainer, and other areas of the site.
I think cell phones will be 'vital' for future (~5 years out) success of chess.com