Wait, I know the author and will share the link so he can join here.
Petalisp author here - this ELS paper is just a preview. I'm also preparing a 160 page document (for my PhD) that will explain everything in more detail. I'll post on HN when it is available.
There is also a recording of my ELS talk on Twitch: https://www.twitch.tv/videos/2138821711?t=00h40m35s