@johnmartin The feature released in the 8/21 release is that multiple dates display on a discussion that has differentiated due dates for different users and sections. The checkpoints feature is currently slated for the third release of the project. Please read through Discussions Redesign Early Access for details.
One of the Instructure Community Managers provided a link for me that I think you'd be interested in taking a look at...if you haven't already.
Under the "Referenced Ideas" heading, you'll find that [Discussions] Multiple Due Dates (checkpoints) for... - Instructure Community (canvaslms.com) is on the list (currently at the very bottom).
I'd encourage you to follow these links and participate in the discussion under Jody's information.
Hope this will help in some way.