A -pages-articles.xml.bz2 to .zim converter would be really helpful, because of the lag between the current database and the zim files. Also with this tool, other users can convert the language what they want and upload it for others, this can save some resources for the kiwix project.
This is not possible to have such tool because the XML dumps contains XML and the ZIM contains HTML and there is no parser except Mediawiki. We will simply try to provide more and more often ZIM file. If you have a concrete need, please make a feature request about it.