An ultimate improvement - to my mind - would be if there was a way to use selection filters ONLY on files in the duplicates list that I've selected (not yet 'marked' in the checkbox, just selected rows). It could be achieved with just a simple checkbox in the "Selection Assistant" window that says "Only apply to selected files". This would make it really powerful and quick for variations on all the selection filters, working on sets and subsets achieved by making easy spread selections based on adjusting the sorting columns - filename/path/date/group etc.
Once again, thanks a lot for the results of your hard work.