LogFAQs > #928541809

DeNA have put out a letter from the producer Satoshi Sasaki and Tetsuya Iguchi addressing many complaints from fans. They have put forth an apology for the amount of problems the game has had, the small amount of content as they thought the current set-up and EX Challenge would be sufficient, but realise that EX Challenges are not for everyone and that they are sorry they brought the game to a point where there was little to do in it.

They detail four different complaints that they commonly saw:
Lack of content
Rewards for stages not being enticing
Level design not being amazing
Game is difficult to understand
With this, they have promised that they are going to change direction with how the game will proceed in the future with more content, more attractive rewards for completing stages and aim to make it so that you can use your favourite Sync Pairs rather than necessarily the strongest for the situation.

They will work on this but state it will take time. They'll provide periodic updates through letters, with the next one planned on October 17th. We'll provide more details as they come.