You didn’t dream, it actually exists 
www.elitefourum.com/t/the-great-grading-results-thread-specials-are-you-joking/13793/1
Edit: I like your idea of comparing your own pregrades with the results. Also nice to see some pics of high grade cards (obviously not all cards of a 200 card submission). Both could be easily implemented any time in the existing thread though if people want to do it 