http://nvidia.custhelp.com/app/answers/detail/a_id/4522
Can anyone install 384.80 hotfix driver and see if it still reports Tier 3 for Pascal & Maxwell?
https://forum.beyond3d.com/threads/direct3d-feature-levels-discussion.56575/page-9#post-1840641
Feature Checker was updated to July 2017 version but can't download it though because B3D forums don't allow it unless you have account with certain amount of posts or whatever.
I'm using the May 2017 version, because I don't have a membership there either, but I can confirm that 384.80 still says resource binding tier 3 for my Titan Xp.
Seems less and less like a mistake, and more and more like it was deliberate.