Very honestly, I probably wouldn't use such a feature if it existed because the existing Search capability in the Media Gallery provides me with the same functionality because of my naming conventions. So I would probably just continue to search for census, wills, etc. as I do now.
A related improvement I would like to see is that the search be hot, and that it would be applied as you type each letter of the search. Searching Source Templates already has this kind of a hot search. Actually, the way searching in Source Templates works, it's more of a filter than a search, and the filtering capability is great.
Indeed, there are a lot of places in RM where I would love to see such a filtering capability. For example, I would like to be able to type S M I T H (except lower case and without the spaces) at the top the RM Explorer index to get a list of all the names that start with "s", then all the names that start with "sm", then all the names that start with "smi", etc. and the filter would be applied live as I type the letters. This would be a true filter so that non-matching names would no longer be in the list if the filter were applied. The Source List,Fact List, Place List etc. could all greatly benefit from such a capability.
Of even more benefit would be if I could change media lists to List mode instead of Thumbnail mode and if it would then remember my setting forever (or until I changed it back), and if it would show the red x for broken links in List mode. That simple change would really be something to write home about. As things stand, I've come to use Tom's RMTrix program to list my media most of the time instead of using RM.