PROBLEM
One very common issue users of LrC have are missing files and folders. Well over 70% of my LrC Help clients come to me with some version of this problem. The existing "Find Missing" tools in LrC work as designed, and many times re-linking one photo winds up re-linking hundreds of other nearby images at the same time.
However in many cases, depending on exactly how the images became missing, one winds up having to manually re-link images one at a time which can be an impossible task if there are hundreds or thousands of such images (a client yesterday had over 11,000).
SUGGESTIED IDEA
In the Import Dialog, add a new checkbox below the "Don't import suspected duplicates" box called "Relink Missing Photos".
If this box is checked and there is also a version of the photo in the catalog marked as missing, rather than importing the image and creating a new catalog entry for it, re-link the existing (missing) photo to the location of the one selected for import.
WHY
Will save copious amounts of time dealing with missing photos.. In most cases where there are loads of missing images, the user used Finder or File Manager to 'restructure' their image storage folder hierarchy. In thses cases, the current physical structure is probably the desired one rather than the one shown in the Folders Panel. Rather than having to re-link folders or files individually, one could go to the Import dialog, and with this checkbox checked could use the "Add" imort mode and accomplish in one step what would otherwise take many days or weeks to accomplish.