Well one problem is that filesystem in general is a terrible abstraction both in terms of usability and in terms of not fitting well with how you design network

Well one problem is that filesystem in general is a terrible abstraction both in terms of usability and in terms of not fitting well with how you design network applications. I’d say Dropbox et all is closer to a good design but their backend is insanely crazy optimized to make it work and proprietary. There’s an added challenge that everything these days is behind a NAT so you usually end up needing to have a central rendezvous server where nodes can find each other. Since you’re looking at rsync where you want something closer to Dropbox, I’d say look at syncthing. It’s designed in a way to make personal file sharing secure.