High on my wish list is to be able to merge group membership when reviewing duplicates. Right now, it seems it is necessary to go through duplicates manually, checking the record summary of each duplicate to see which groups each belong to, and then manually dragging the kept duplicate into the groups to which the deleted duplicate belonged - this is a long & tedious process - something that could easily be automated, I believe, even just by showing group membership in the “Find duplicates” dialogue box - so that they could be copied and pasted between duplicates, similar to the other fields.
This would be a huge help!