This is closer to a shower thought, given I don’t really know much about how ActivityPub works. Has anyone, or is it even possible to, made an instance designed to work as say a FUSE file system?
I was mostly just thinking about how hard UIs are to make and thought “what if the content was the UI”.
The thing you’re looking for exists and is called IPFS. Imagine fuse mounting BitTorrent. Actually, the fuse part is a minor feature, but it exists.