Any news about this?
The solution here: Remove duplicates seems to me too much difficult to use. Just simple filter setting that would allow filter non-unique (and may be also uniqe as an option) data in selected field (column) would be sufficient.
As the unique/non-unique information already exists (in footer, when selected), its implementation shouldn’t be a problem. (And if the field is text type, then also case-sensitive checkbox could be added…)