Multi-Language Support
A great feature for a number of sites is vBulletin's language and phrasing system, because it allows them to translate their forum so that users from different countries can enjoy the site's content.
While it is currently possible to translate all VaultWiki phrases to a forum's single language of choice, adding Multi-Language support would allow the titles and text to be available in other languages as well.
This is not a change that can be made quickly. It would involve reorganizing the way namespaces, articles, and revisions are each cached, how they are saved, and how they are retrieved. As a result, this feature must be pushed to the next major subversion.