the 01.7 release of MkDocs includes support for themes to extend other themes. Rather than needing to "generate" the themes here, I wonder of inheritance should be used instead. In fact, I expect that these themes could all extend the mkdocs theme. That way, they would get any (non CSS) updates automatically. If, for some reason, they can't extend the mkdocs theme, they should be able to extend on of their own (set one as the base which is a complete theme and all other extend it only providing the files that differ). I accepted this PR anyway because it included CSS changes which still needed to be made, but using inheritance should cut down on the work to keep things up-to-date.
As per https://github.com/mkdocs/mkdocs-bootswatch/pull/36#issuecomment-348969706: