tweeted in his twitter (@angelfrench) that the length of Kami nomi zo Shiru Sekai
TV series depends on the reactions of the viewers (i.e. the sales of the DVD and other media).
ryohayate2409sa: @angelfrench Is it one season long?
Wakaki: It's up to the reactions. I wonder how many episodes it will take until we see Tenri
DiceKatKobe: @angelfrench What do you mean by "reactions"? Should we send emails to the TV company?
Wakaki: Frankly, the sales of the DVD determine everything.
Wakaki is anxious about the poor environment of the anime creators. "In the case of manga, the author can improve the quality of the work and make money by his/her private effort, but anime creators' efforts never pay.", he said. "I've learned how hard the anime production is, so I'm seriously thinking about how to sell it."
Sources: Wakaki's twitter