I believe I've answered a similar question before, but it's somewhere on the forums, so it's understandable if you've missed it. I want to expand on the Books FAQ to include some common questions like this in the future, but for now:
I'm a bit reluctant to add release dates, since that's one of the thing we were too optimistic about when we first started out. It's not fun for anyone when a (early on unrealistic) deadline is missed. However, for the last six months or so we have been meeting our internal deadlines for all the book releases, so I think it might be possible to start listing more precise release dates. Currently we only list the quarter for a title if we have it planned for release—for example,
BoBoBo is scheduled for Q1 2016, so it should come out at some point between January and March—but I hope we can narrow it down to at least the month in the near future.
As for how often we release a new book, we've been putting out a new one every three weeks (last one was delayed a week because of the holiday season), and we aim to continue at that pace.
Kira Kira pre-orders went up a week ago, so the next will be early February.