Some suggestions that would make the finding similar files function in XnView easier to use:
- The ability to sort results by similarity. There is already a function for this, but it only sorts by similarity within duplicate results; I would like to be able to sort all results by similarity and e.g. have the closest matching files on top
- The ability to select and delete multiple results and/or delete all duplicates, either by smallest filesize or smallest resolution (suggestion is similar to here)
- One way to make selecting/deleting multiple results easier would be the ability to switch views between the current gallery/comparison view and a list view similar to that used by DupeGuru
- In the comparison viewer, an option to not have the two files side by side, but instead show them in the same position in an alternating fashion. For instance change between image 1 and image 2 by using the left/right keys, or by mouse-over. Or perhaps an image comparison slider. If the duplicate images are shown in the same position, it's much easier to spot differences e.g. in image quality, cropping or effects used than when they are shown side by side.
- Performance suggestion: the ability to use multiple cores/threads when scanning for similar picture content, to speed up the process on larger image sets
- An option to scan videos and compare them by content; e.g. taking the first frame of every video and including it in the picture content search. I guess this is how it is already done with animated GIFs
... Almost like filtering by similarity... 
