Reduce the demand for it. Include easily accessible "article only" mode, make your site friendly to current Reader Modes for all major browsers. No obtrusive ads, no 500 trackers bogging down the browser. Quick loading. Just give us the info we need, nothing more. Just like ad blockers were a response to websites not respecting people's attention and safety, likewise AMP is a response to them not respecting people's time.

Does anyone around here actually know how to make sites friendly to iOS safari reader mode? Last I checked, it wasn't documented, and the best wisdom floating around was something like "use divs and maybe an article tag or two"

I've no idea about Safari's reader mode, but you can have a look how the readability feature in Firefox works: https://github.com/mozilla/readability

I'd expect the Safari feature to work quite similar.