Especially for things like Python's embedded SQLite. Packaging and loading an extension module cross-platform with an otherwise pure Python script seems difficult.

JSON1 is compiled into every Linux distro's SQLite I tested and is also in Mac's SQLite, as well as the Windows binaries provided by sqlite.org. The only exception I found was the SQLite bundled with Python for Windows, which doesn't seem to have any extensions at all.

Performance-wise this is fast enough that you can do faily complex un-indexed queries (so full table scans) against tables with a few ten-thousand to hundred-thousand rows and have them complete in a couple tens msecs.