@Divingduck: I changed my mind and decided to add some code to the docx input plugin to try to figure out the correct css properties for fonts in docx files, when they are present on the computer during comversion. calibre already maintains a font cache. My main concern was not the performance, but the non-reproducability (the results fo the conversion depend on the fonts isntalled on the system -- but on further reflection, I think it is worth it)
See
https://github.com/kovidgoyal/calibr...9fe21c422fa642