About a year ago, he shared that he had a draft of a new book on "Communication":

https://people.csail.mit.edu/phw/favorites.html

Was this ever finished?

It was!

It's in the final stages of publication — I've seen an editor's print in its final form — although I'm not sure what will happen to it now. I would guess it will still be published.

You seem close to someone who will announce the publication. I would be grateful if you would post their announcement on HN when the time comes.