I am sorta sure it got mentioned again after the Gerrold book, possibly in an early STARLOG, but there sure as hell was no book that saw print.
Then again, how many books have you seen that say 'soon to be a major motion picture' on the cover that either never become a major anything or don't hit movie screens till the book is 30 printings and 10 years downstream from the announcement?
When FLETCH said soon to be on its cover in the 70s, I was thinking James Coburn if they went old, Tommy Lee Jones or Tim Thomerson if they went very new. By the time FLETCH went to movies it was the better part of a decade past.
Indeed, many books are optioned, but few are filmed. It's not uncommon for a book to be "Soon To Be A Major Motion Picture" for decades.
Anybody remember the movie versions of THE DEMOLISHED MAN, MANHATTAN GHOST STORY, SANTIAGO, or COLD WAR IN A COUNTRY GARDEN?
I've always felt you shouldn't hype the movie version on the book cover until the movie actually starts filming, but sometimes publishers get excited and jump the gun . . . .
And, getting back OT, occasionally books get announced that end up never being published, or finished, or even written!