After finishing a game, a possibility to replay the game (move by move) would be great. Very useful for learning from the game and possibly analyzing what was done right and what was done wrong. It would also be great if such replays were made public so that one could learn from better players.
This is on my longer term plan by which I mean it’s not just somewhere in a backlog, I am definitely working my way to it. I had this in mind when designing the database schema many months ago.