Hi Joe, I've put 2.3.6.4 into development, and tried out the new parent page hierarchy navigator. If I pull up an existing page and browse for parent, it shows the full site hierarchy, but if I create a new page from scratch and immediately hit the browse button, it only shows Root as a choice.
If I'm doing something out of order, or missing any styling or other settings that might be affecting this, just let me know.
Thanks,
Jamie