Wiki Index item is always displayed in Drawer Menu, but in some situations this link cannot work: Because it leads to a parent (XEM) wiki, without proper access rights the wiki index page will be not displayed.
It would be nice to display the link selectively, e.g. if the user is local (doesn't exist in XEM wiki) and XEM wiki requires login, to don't display it.
I am not sure how complex such enhancement is and possible performance drawbacks. If it cannot be implemented, as an alternative XWiki Preferences should be extended by a switch "Display wiki index link".