I just sent a message through the MythSoc list about this publication, first(?) noted by Dorwiniondil over at the LotR Plaza (so some of you may have already heard about it):

Collectors should make sure to pick up a copy of the forthcoming The Times Literary Supplement, 14 September 2012! It features an article about the artist Mary Fairburn by Paul Tankard, who quotes extensively from formerly unpublished letters by Tolkien.