Respawn has tweeted out stating that they have finally decided the reward for those who have completed the original Gooser Challenge, which took 50 to complete. Respawn states that the reward will be a special titan emblem, which can be customized on to your titan in the upcoming update.
@JorianHull special Titan emblem coming in the next update
— Respawn (@Respawn) June 12, 2014
No release date for this update has been announced as of now. Stay tuned.