It seems the sax syllabus last changed in 2006 so it'll probably be another 3 years before it changes again (assuming they always run for 5 years).
I don't know if they're planning to bring out the grade books. I think it would be useful if they started doing this for all instruments and all grades as it gives people the option to only buy one book. I guess they may do this for the sax syllabus at the next change.
Lucid
EDIT: I've just seen that the syllabuses don't always run for 5 years at a time. In that case I don't know how long it will be until the next change, but maybe no longer than 3 years.