For a quick example, NPD just called it this (8th) generation. Do you have anything showing it to be 9th generation?
Neither NPD, Nintendo, Sony, Microsoft or third parties use the terminology that is used on forums. For example, you won't find any of those five entities call the PS4 an 8th generation console.
The terminology that is used on forums ties in with how console generations are listed on Wikipedia, which is a website with user-made content, so ultimately it's a feedback loop where forum goers and Wikipedia editors go with popular opinion. That's why Switch is currently listed as 8th generation despite being 9th generation. But if the Dreamcast is recognized as 6th generation despite discontinuation before competing against other 6th generation consoles, then Switch will eventually be recognized as 9th generation because it will actually sell alongside the next PS and Xbox.
Guess why the Dreamcast is considered 6th generation. It's because it succeeded the Saturn, a 5th generation console.
It's also worth remembering that the 3DS wasn't categorized as 8th generation right away. Once again, because forum talk casts judgment.