When selecting files within new torrents, or viewing files in in-process ones, it would be nice to be able to sort files by extension. We can already sort by name, bytes downloaded, whether or not a file is selected already, and a couple of others, but the ability to sort by extension would be helpful. For example, audio torrents from Archive.org often include multiple copies of a given audio recording in different formats: .ogg, .mp3, .m4a, and in the case of recorded lectures, there could be >40 individual recordings. It's tedious to have to sort through a list of 120 files to select only, e.g., the .m4a files. Thus, the advantages of sorting by extension. This would also be helpful in music torrents that include .jpg scans of CD booklets, or TV torrents that include dozens of episodes plus multiple subtitle files for each episode.

Four years later and this would still be useful to implement

you could use the file filter to look at files that end in say .mov or any extension.