A little out of school talk here, but if you're wondering why this one is taking is long, let me point out it's the book on religion and churches in a series called Echoes of Heaven (I point this out to Defendi whenever he mentions how much extra work it's requiring).
It, very possibly, contains as much or more (my gut says much more) firm information as the entire Setting guide. So the production-level reason delay is that with so much stuff, producing a quality product requires a lot of work.