With regards to what was mentioned about spam and spam handling towards the end of the article, I’d recommend listening to the last Libre Lounge episode, to find out what methods are being considered in that area.
It’s sitting on my phone waiting to be listened to.
I found https://flak.tedunangst.com/post/the-activity-person-examined valuable for highlighting some places where compatibility and compliance totally break down—useful when building other specs. I think I see a pattern of this happening around overly-flexible parts of the spec. Implementations don’t actually comply with the flexibility, and instead just hard-code the cowpaths.