It is a very strong security risk: anyone who compromised any active account in this wiki may insert arbitary HTML, which may be loaded by everyone visiting the site. Raw HTML are mainly used in many outdated and historical pages, many may be migrated to non-raw HTML (e.g. wiki syntax and TemplateStyles), and I don't think it is essential for this wiki as it is not a public portal for Wikimedia Foundation anymore.
Once it is done the wiki may possibly be made open.