I can also tell you that the book is being edited by Brendan Wolfe and will feature a foreword by Sir Anthony Kenny. The nephew of Alexander Jones, general editor of The Jerusalem Bible, Kenny had a first-hand perspective and may be able to offer one or two interesting morsels. He described a meeting with Tolkien about the project in his memoir, A Path from Rome: An Autobiography (1985), calling Tolkien “a difficult collaborator” .
According to the marketing collateral DL&T sent me, “Kenny [in his foreword] recalls his own memories of working on the Jerusalem Bible and the impact made by its groundbreaking publication” — no mention of Tolkien there. But then:
[Editor] 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.Just what form the exploration of these resonances will take — whether an introdutory essay, footnotes, commentary, or some combination of all of these — we’ll have to wait and see. I still have a difficult time imagining how the book will be more than a hundred pages.
And finally, as to the question of the translation itself. The marketing collateral sheds little light, I’m afraid. It refers only to an “[e]xclusive translation”, calling the book “[a] beautiful new presentation of one of the best-loved Bible stories in a translation by J.R.R. Tolkien.” Note that the credit for the translation is here given entirely to Tolkien (pace Carpenter). Moreover, “exclusive” does not mean new — it may simply acknowledge that the trans-lation is and has always been copyright DL&T. The flyer gives no indication whatsoever of any material by Tolkien not previously published. It’s probably safe to assume there won’t be any. Update: Or perhaps there will be. See the comment from Jeremy Edmonds below.
One final note: this isn’t the first foray into the world of Tolkien by DL&T. They’ve published one previous book about him — Stratford Caldecott’s Secret Fire: The Spiritual Vision of J.R.R. Tolkien, a 160-page  monograph examining Tolkien and his works from a theological vantage.
 Kenny’s memoir is cited both by Scull and Hammond in their Reader’s Guide, and by L.J. Swain in his entry on “Judaism” in the J.R.R. Tolkien Encyclopedia: Scholarship and Critical Assessment. Ed. Michael D.C. Drout. New York: Routledge, 2006, pp. 314–5.
 This figure is from the DL&T website, where the book is apparently still for sale for £9.95; however, according to Amazon, the book is only 144pp. and is no longer available. Has anyone read Caldecott’s book? I’ve read one or two of his essays, but not Secret Fire.