- Official Post
It might be technically possible to do some of the things you state, but the primary reason for migrating/regenerating the DB between Kodi versions is that it makes Kodi developement and support easier. The all-volunteer Team Kodi staff needs to strike a balance between spending their limited time on coding new features and fixing bugs .. and multi-version backwards-compatible SQL database support has "huge amount of effort for little reward" written all over it in mile-high flaming letters. Throw in "MySQL vs. MariaDB" and DB versions for extra hassle.
I know people have tested Krypton migration and I would expect a few to have done Jarvis, but I doubt anyone on Team Kodi has tested migration from as far back as Isengard. The reality is that developers develop on v.next not v.old and the staffing is limited; there's no QA department
NB: The Kodi wiki has some workarounds for DBs that fail to update including "export and reimport" if that's needed.