> What would be the use case for this?

Quoting D. Richard Hipp, from the sqlite-users mailing list, 2018-03-18, FWIW:
  These APIs support the concept of using small databases (small enough 
  to fit in memory) as a container for passing information around. 

  For example:  A client program might communicate with a server using 
  an HTTP request and sending an SQLite database as the POST data.  Or 
  the server might send an SQLite database as the reply.  [...]

  Advantages of using an SQLite database as a container: 

  (1) It is easy to mix text and binary data without having to worry 
  with encodings. 

  (2) Applications can be easily enhanced and extended in 
  backwards-compatible ways by adding new columns and/or tables. 

  (3) Easy to manually view or modify the container content during 
  testing and debugging. (JSON also has this property, but JSON does not 
  work with binary data.) 

  (4) No need to write encoder/decoder logic. 

  (5) There is a high-level query language available to extract the 
  content in an order that might be very different from the order it 
  appears in the file. 

  (6) No need to worry with big-endian vs. little-endian translation, 
  nor UTF8 vs UTF16.  The database handles that automatically.


Using the serialise/deserialise API's to pickle an in-memory database to a data stream is an interesting thought.