There are probably a ton of projects that depend on libjpeg-turbo, but the first thing that comes to mind are browser vendors. It's probably fair to say that most jpegs are viewed in web browsers. They should really just chip in, or even formally employ the author to just continue working on this library.
FWIW, Mozilla has been maintaining their own fork for quite a while now[1]
But AFAIK most Linux Distros have been using libjpeg-turbo as a drop-in replacement for libjpeg, after some drama in ~2010 where libjpeg came under new management, decided to break ABI/API several times over and add incompatible, non-standard format extensions[2].