MediaWiki is often used as a framework, so when talking about turning it into a library, comparing with what the Symfony framework did could be helpful. They extracted most of their code into libraries called Symfony Components which now have widespread adoption in the PHP world. I imagine you would want to do something similar for MediaWiki, as a single big "MediaWiki library" does not make a lot of sense if you ask me.
PS: thanks for pushing this stuff
Yeah, Symfony was part of the motivation for writing this, but I tried to approach from a product perspective rather than a technical one: what are the qualities that make MediaWiki a successful piece of social computing software and to what extent can they be separated from the traditional concept of a wiki? Could some of the internals of MediaWiki be used to make an arbitrary website more wiki-like? (Can we provide "wikification as a service"?) What architecture could enable that?