Further details on The book of Jonah are beginning to come out, so I will summarize here as best I can.

The book is currently targeting an August release, not July as reported by Amazon.

There is a Foreword by Sir Anthony Kenny, where he "recalls his own memories of working on the Jerusalem Bible and the impact made by its groundbreaking publication." This memoir has evidently already been published, as it (or another version of it) is cited by Hammond and Scull's Reader's Guide and Drout's J.R.R. Tolkien Encyclopedia: Scholarship and Critical Assessment in the Judaism entry by L.J. Swain (pp. 314-5). [Thanks to Jason Fisher for these references]

The main text is edited by Brendan Wolfe. From the publisher: "Brendan Wolfe tells the little-known story of how Tolkien, then at the height of his fame as the author of The Lord of the Rings, agreed to join the team of Catholic writers and scholars working on a major new translation of the Bible into English in the early 1960s. The result was the Jerusalem Bible, still celebrated for its elegant, timeless English. Wolfe shows the resonances between the story of Jonah and the whale, Tolkien’s contribution to the JB, and themes in his other writings."

The publisher also confirmed to me via email that "[t]he book will include unpublished material which was not used in the Jerusalem Bible as published in 1966." Also the Advanced Information flyer states "Newly available material from one of Britains most celebrated authors."

Darton, Longman and Todd, the publisher for this new paperback volume, are the original publisher of the 1966 Jerusalem Bible as well. The issue of copyright (especially for previously unpublished materials), attribution ("translated by J. R. R. Tolkien") and permission (the Estate was unaware of this book until today) may still need to be settled.

Trotter update

This book was not published, if you are interested in the Book of Jonah, then try and get a copy of the Journal of Inklings Studies Vol 4 No 2 (October 2014) which has Tolkien's translation and commentary.