I just found out about this one through Sacnoth's Scriptorium, the blog of John Rateliff, the author of The History of The Hobbit. There's not a lot of detail yet, and almost none of it (other than the cover and release date) is on Amazon.com.
The book is:
Mcfarland and Company
Release Date: May 15, 2014
According to the blog entry, the essays are all by Tolkien fans. To date, the only essay I have any information about is the one by John Rateliff, and his essay is titled: Inside Literature: Tolkien's Exploration of Medieval Genres.
Shippey was a noted Tolkienist himself, with the books The Road To Middle-Earth: How Tolkien Created A New Mythology and J.R.R. Tolkien, Author of the Century.
As always, another book to look forward to.