For some weird reason the thought crossed my mind that the slowdown in Rich's updating was a result of "loosing" the instant update buzz from enworld.. But then I thought, maybe it's because we are now in CON season.
It's not burnout. It's the end of the next book. Some say 672 will end it but I think 671 was the end of book episode. Obviously we won't know until the book is compiled. But the last few strips have been quiet because he's already hit the climax of a book and now we start a new chapter and the strips should start being "important" again.
I also doubt it is "con season" as Rich rarely attends cons. Again, at the end of a book he usually takes it slow or even takes some time off.
(I'm not speaking for Rich. Just sharing my observations of how's he's worked in the past.)