Example, to run Monica locally you have to run a MySQL server. This seems .. a lot, for the average user. It also exposes hardening issues, backup concerns, upgrades, etcetc. I want to stress i don't blame Monica here, there are almost no alternate options.
SQLite is the only thing i find really great, but that just covers SQL.. and frankly i still want more even from my SQL layer. I'd love a very, very resilient storage mechanism for users. Something easily backup able. Easily merge-able in the event the user accidentally forks backups[1].
I often think i want something like Camlistore (Perkeep). Something that can store both structured and unstructured data (sql/files/etc). Something versioned, easily immutable. Something users can rsync around without fear of losing/corrupting anything. Something that apps themselves can push around for automated backups to cloud storage if desired. Super, robust. Something that doesn't require running any servers - just run the app.
I know a bunch of people are working on immutable databases, but i often see them (DoltDB) focused on being MySQL but with Git. I think i want Camlistore - a true data-dump for end users, but with better interfaces for App developers. Eg give app developers a true SQL interface, with a dumb file interface, etc.
I'm working on my own solution for this, but i doubt it'll be anything more than a toydb. I hope someone with great skill solves this problem :)
[1]: Merging is never easy, but some systems can definitely make it easier or more complicated.