Just a note for anyone else trying out this awesome new feature:
— After update, I had to deactivate and then reactivate the URE plugin to get the “Nav Menus” control to appear.
–Also since we are using two different menus in the same location depending on page template, I did have to at first leave un-blocked both menus at that location and then block the unneeded one after the admin view populated with the value for the menu that I want the user to only have access too.