regarding multiple writes - I think hardest part would be to find an sqlite version where "read is a combination of all the files".

Speaking of multiple writers, I've recently heard about "BEGIN CONCURRENT" feature of SQLite [1] - currently it lives on its separate branch, but I hope they will eventually merge it to the main branch. Not sure if it can be used in your case, but worth mentioning anyway, I think.

[1]: https://www.sqlite.org/cgi/src/doc/begin-concurrent/doc/begi...

Not sure I understood your question fully, but if there are multiple versions, then read will be over multiple files but writes go to a single active version.

Each writer can get its own branch but you would never be able to re-combine them.