Oh. So that's what they meant by "variables support" in the ssl directives. I didn't realize the significance of that change when I read the changelog earlier today.
What is? Looks like the link goes to a changelog and nothing else.
The original title for this item was "Nginx 1.15.9 adds support for dynamic certificate loading" which explains why this is interesting, but then someone edited it to the current less useful version ¯\_(ツ)_/¯