What exactly are you aiming to get out of Game Center?
I just finished a google play plugin that enables Leaderboards and achievements much like the Game Center. Though it does not have quite as many features as the game center plugin.
I may make this, I currently plan to try to make at least 1 or 2 plugins a week as I need some supplemental income. With that being said I have a few requests stacking up. I am just finishing up the Play Store then I will either be working on In App Purchases, AdMob, Game Center or Neatplug Facebook and Twitter.
Something like AdMob can be done in a day. Though Game Center or In App Purchase plugins take several as they contain so much content.