I would like to suggest endpoints for accessing player statistics. Such as:
Ratings for the various game types -e.g, Daily, Rapid, Blitz-, and various stats for each game type. So, timeouts for daily games, perhaps Glicko RD, and the percentages of wins, losses, and draws based on colour.
Also, would it be possible to get historical ratings in JSON? Maybe adding a "start_rating" and "end_rating" for white and black in games from the "Monthly Archives" endpoint?
Edit:
Though, thinking about, I guess that last part about adding a start and end rating really is not nessecary. Silly me.