It occurs to me that a useful halfway (well, partway…) house here might be just some simple sync mechanism between a PWA offline database and a desktop computer.
Maybe this? https://pouchdb.com/learn.html
But still, I’m very dubious something like that is yet accessible to all but a tiny tiny fraction of users 
(if only sandstorm.io were still being developed seriously…) Who’s going to run Couchdb on their Mac / even linux box? Many, many fewer people than might be willing to sign up to a generic host-my-data-away-from-google web service, I think.
Edit: apparently there’s life in sandstorm.io yet https://sandstorm.io/news/2020-02-03-reviving-sandstorm