> 1. App views decide permission parameters for their modality and frame the user experience

Yeah, so this is the problem. A system flexible enough for that will be some combination of centralized, hilariously over complicated, massively inefficient, and full of odd unexpected behaviors.

Perhaps if you are after public square social media. If you are after small social media, the usage patterns and tradeoffs look different.

Modded Minecraft (smp) servers are interesting prior art for me.