One assumes they will UA two for each class, so we are due another sorcerer, bard, cleric, druid, ranger, artificer (I reckon the main motivation for doing the book now is to reprint the artificer for people who don't like Eberron). The rate of release seems to be stepped up - 2 at a time, 3 at a time, 4 at a time, suggesting the date of content lockdown is getting closer. But there is still quite a long time between content lockdown and publication. So my best guess is this book will come out in September, +/- 2 months.