Syncthing solves a large part of syncing data between devices using your own VPS, server(s), etc. If your VPS provider goes out of business, you can then just fire up a new VPS and hook it back up to your local machine(s).
Thing is, like Syncthing, it lacks a collaborative feature. Nextcloud has it, but only if you have the Nextcloud accessible (I want to host only on LAN). Something like IPFS (or Tor) is a solution to such problem.
It does not, you can share folders with anyone you want without them even needing an account.
It would unlock scenarios like share your files with me and I'll share files with you and neither of us will know the others files unless your house burns down in which case you can get your files back just by hookin the sync back up with the encryption key pulled from your password manager.
With Syncthing I don't (yet) have this problem.