In what really comes as no surprise to anyone who has followed the Final Fantasy XIV trainwreck, the game is now effectively dead in terms of player population. A blogger in Japan did some research into the current connections to the server and discovered that the total number of players each day is pretty abysmal. You can find the information here, in Japanese.
Basically, Final Fantasy XIV has only 17,000 unique connections to the servers every day. That means only about 17,000 players are actually playing the game now. The 31,000 number on his list is the total number of characters, which include alts and mules, while the 17,000 number is the actual unique number of players.