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”.
No, the latter is done via a DHT, while the former is a layer on top of IPFS (Filecoin, I guess, as verdare said). Default IPFS behaviour is that you just cache whatever you download, and serve it to others if they request the same file from the network. Basically a huge bittorrent kinda thing.