How to give feedback for an Apple app not listed on the Product Feedback page?
After suggestion from @user3439894, I had tweeted Apple Support and here is their answer:


  We love feedback. If you don’t see the Apple app you wish to leave feedback for, you can leave feedback by choosing the device you are using here: http://apple.co/Feedback


So, following that, I had posted the feedback using one of my devices as a channel, explaining in notes why am I using the device channel, and also listing all the OSs that I mean this feature request for.