Just talked to Scholastic today and got the current 2009 schedule --
It looks at this point like there will be a total of five books in 2009, three the young readers and two chapter books (potentially larger than the normal ones, but don't know yet) --
The readers would be out in January, April, and September, with the chapter books out in summer and fall. The hope is that between the buzz the readers are generating among the retailers (apparently, they are going to get into some big stores that the chapter books currently do not), the increasing sales of BIONICLE and the movie coming, and the chapter books being more of "event books", that chapter book sales will go up and we will be able to do a more extensive schedule of them in 2010. Scholastic does not want to abandon them, but sales continue to be in a trough for them, so right now the two is the best they can manage for the schedule.
I will still be doing them, but will probably also be spending some time on my own, non-LEGO writing, since the readers don't take much time to do.