Although I like the monthly updates, the biggest drawback for me has been the lack of a new Sonar Power book. Scott's descriptions and explanations tend to be clearer and more helpful than the manual or help files. The books have always been the first place I check when I need to understand learn how to use a particular feature. Also, there's just no substitute for a hard copy book, for me at least.
I wonder if it would be possible to come out with something like Sonar Power 2016, as suggested by Resonant Serpent, followed each year with an addendum that covers only the features added during the subsequent year.