If it isn't a big enough need to inspire a Sigil plugin, do note that calibre already supports DOCX as a Conversion Input/Output. So you could always use calibre to convert
to DOCX.
(Granted that it could replace this plugin too, except it is nice to have an alternative that doesn't require yet more software. Still, a DOCX Export plugin doesn't seem nearly as useful, so who's going to make it?
At a certain point, we are getting beyond the purview of Sigil.)