On May 09, 2015 I replied to the e-mail from the support, quoting the acquisition procedure of the gog.com key for developers by JudasIscariot. So far I did not receive an answer from the Double Fine Productions Support Team.
Today I checked the backer download page (humblebundle.com) again. To my great surprise it now offers an option for a gog.com key. I immediately redeemed to code at gog.com an am now in the progress of downloading. The code was valid till May 10, 2016. So the information from Gydion might
have led to the very positive outcome for me and some other backers. Thank you very much Gydion!
One year ago Double Fine Productions informed about the Ouya key via e-mail. Maybe they'll sent out an e-mail to inform the backers about the gog.com key. Maybe they don't mention it, as it is a bit late, as most backers accepted the fact of a missing gog.com key after two weeks (or more than three weeks without the official announcement).
Anyway I am thankful for the final outcome and will enjoy now my first backed game.