As you've discovered, Bose lead the way in ANC. The way to know if there's a new model coming, is firstly to check the release date of the current one, and secondly to see if significant price cuts across retail are coinciding with the release schedule.
Failing that, or at least not being conclusive enough to make a decision, check retail at the usual seasonal sale periods. You can do this historically for additional info.
Don't forget to check the manufacturers website as well.