Well the S2 is just an S1 with more chips per GH/s and the chips slowed down to get the W/GH down.
So unless they decided that the S1 chip is the end of the work for them, they certainly must be working on a next gen chip ...
I read somewhere that Bitmain will sell 40nm miners in April and 28nm miners in July. The price of S2 batch 3 will be reduced much?