I am guessing that the recent sale, which appeared to bring in a lot of new players and a lot of new feedback (which in the long run is a good thing imo), is something that the devs will want to digest before releasing the next beta, especially as regards game stability, i.e., crashes and freezing. I am also guessing that the timing of this sale wasn't necessarily what SD wanted...Steam offered to feature GC3 and they could not say no. Again, a guess.
That said I think third or fourth week of March is a reasonable guess, as Lucky Jack says.
