I asked Peter Blood about this last year. The second Rise Up Singing book is definitely a work in progress, but don't hold your breath, it may be a couple of years yet (don't have a recent estimate).

The first RUS took a long time due to the necessity of getting all the copyright permissions, above board. The second one is no different in that regard. So keep not holding your breath.

The good news: he also said they're going for more rowdy, bawdy, perhaps even politically incorrect material. So it'll seem less like the ultimate hip Quaker hymn book.

W-O