You know when you go to a movie and they show the previews under the heading "coming soon?" They could just as well say forthcoming, because it means the same thing. Only who would want to see that stuffy movie?
"Forthcoming with" means "providing"––if your neighbors are not forthcoming with candy on Halloween, you might have to egg their house. When parents complain that their teenagers are not forthcoming with information about their life at school, they should remember how much they valued their privacy when they were their kid's age.