This feature was talked about earlier this year, but it now looks like that Grader Notes will be included in PSA service levels Express or higher. PSA terms and conditions now reflect this:
https://www.psacard.com/termsandconditions
I am very excited about this new feature and what information the grader will provide. And of course, now that SGC is under CU, I hope SGC will also provide this feature in the future.