According to the latest GMT Games customer update, its been delayed to at least February:
January 24, 2016 Update from GMT Games wrote:
1. When will the Yearly Sale happen? Right now, we just can't handle the mass volumes created by the yearly sale with our existing systems. The work on the new systems is proceeding much more slowly than we'd hoped and planned, and that is delaying our yearly sale. My plan at this point is to run the sale about two weeks after we have all the new systems in place and tested. Unfortunately, I can't yet tell you exactly when that will be. We're testing some new P500 code from the programmers next week - and that's been the big holdup - so hopefully we'll be able to make more progress quickly after that.