Build a simple system around "content groups", something that people will put in the same mental category as "group chats". Each "content group" has a LUKS encrypted filesystem somewhere in the cloud. Keys are exchanged using Megolm and Matrix rooms. The filesystems are mounted via sshfs and decrypted locally. The "pin" is replaced by membership in a Matrix room.
The cloud never sees the LUKS key, and the tagging is done locally. The cloud back-end can be changed using the Matrix control channel, so you're not locked in to one vendor.
I really don't think people will buy in though. At this point, no one cares if their whole life story is recorded by FAAMG.
I'm also interested, details on my contact page. I have a lab and hardware and a decent internet connection.
There are certainly also specific UX/functionality differences on how the apps are implemented, but those are probably the macro considerations.
My take on self-hosted services (not infrasructure, though) is layperson-friendlyness. See https://mro.name/ShaarliGo#install--update or the 5min talk I did a while ago: https://txt.mro.name/34c3 (that page isn't layperson-friendly, but you'll make it)
anyone?
I think honestly the problem is that these systems are not consumer-oriented products. I think there is a real desire by people to not have to live as rentiers in the digital marketplace, but there are not really products that cater to that.
IMO There's a place for something that merges a NAS, with some sort of overlay over current IP that is encrypted and fully peer-to-peer. But NASes are still too hard for many consumers to set up, and most techniques to overlay over IP are likewise too difficult, and basically impossible to correctly multi-tenant (you can't share your network space with your aunt and your coworker without sharing with both). Unlike IPFS, or bittorrent, availability is important, but not critical, and you don't need to promiscuously replicate your information across the entire world, encrypted or otherwise.
I think there's a market for something that is like "plug in to your local network, do minimal configuration, you can set up shared folders a la dropbox, and you can access it over the net". You can sync credentials with a username and a one-time PIN. You should be able to easily set up rules for sharing with friends, with smart defaults.
I think what's interesting from a consumer perspective is that there are things you can do on such a platform that many (not all) people would think twice about letting facebook do, like tag and organize photos of your young kid and share them with relatives/friends who have a PIN.
I also think that the time horizon for this is relatively short (5-years?) soon people will be so desensitized to advertisements/being a digital rentier that the opportunity will have aged out. 20-somethings don't know what a NAS is.
I haven't started on this yet, but if anyone is interested, my info's here.