@Daan Patchwork ¯\_(ツ)_/¯ I was going to just try and find out.

Oh, actually this appears to clarify some things I was going to speculate about: https://sqlite.org/forum/forumpost/fa6f64e3dc1a5d97. The bit about migrating seems too magical to be true:

Just start writing out JSONB for new entries. The old entries will continue to work. The new entries will just work faster.