A feature that would be welcome is to make tag changes visible in the history tab. As of now, there's no way of knowing if tags have been changed or removed, and by who. This means that anyone with the access to edit pages can also edit or remove some or even all tags on a wiki without it registering in either recent changes, the history tab, or in meta data.
This is a serious flaw in my opinion, and for anyone affected, you really need to look into a way to redesign or fix this security hole. One way would be to make tag changes visible in the history tab, including who edited them and when.
An alternative solution to this problem would be a "Permissions" setting, where you can decide who is allowed to edit tags, so that you can restrict tag edits to, for example, members, moderators or the admin only. That way only authorized personnel will be able to change or remove tags.
