Says the man that started this …
You were right then, and still are, although you seem to be a little bit behind on Thunderbird itself, because its current database is SQLite.
Anyway, it’s an old wish from me too, to read the address book, to import mails and convert them to sources/citations, based on the idea that every email has an author, and a title, that can go the source, and every individual email has a timestamp, and could be assigned a sequence number, both of which go very well with the existing fields in the citation, which can then hold the email text in a note.
The only drawback here is, that when I can have a choice, I’d rather use the author as a source, to group all conversations with him or her, but for that I’d need a title field in the citation object, or abuse the vol/page for that. And the latter part goes very much against my autistic mind.