Seems like it's asking to be forked
It has been forked at least once:
The real fork is DuckDB in a way, it has SQLite compatibility and so much more.
The SQLite team also has 2 branches that address concurrency that may someday merge to trunk, but by their very nature they are quite conservative and it may never happen unless they feel it passes muster.
https://www.sqlite.org/src/doc/begin-concurrent/doc/begin_co... https://sqlite.org/hctree/doc/hctree/doc/hctree/index.html
As to the problem that prompted the article, there's another way of addressing the problem that is kind of a kludge but is guaranteed to work in scenarios like theirs: Have each thread in the parallel scan write to it's own temporary database and then bulk import them once the scan is done.
It's easy to get hung up on having "a database" but sharding to different files by use is trivial to do.
Another thing to bear in mind with a lot of SQLite use cases is that the data is effectively read only save for occasional updates. Read only databases are a lot easier to deal with regarding locking.
SQLite is fairly fork-resistant due to much of its test suite being proprietary: https://www.sqlite.org/testing.html