The H. P. Lovecraft Cat Book now has a Necronomicon Press pre-order page, a cover and TOC, and a release-date of 20th May 2019 for the paper editions. The hardback first edition is limited to 100 copies.
“assembled by S. T. Joshi … lavishly illustrated by Jason C. Eckhardt” in pen and ink.
I’m assuming that “The Cats of New York”, listed in the TOC, might be something drawn from the letters? Or perhaps a scholarly essay from Joshi on the cat-encounters? We also get an “Extracts from Letters” section, although at present it’s unknown how completist this is.